When Antonius and the ponies arrived at the library, Twilight immediately started to get busy with the checklist she had mentioned earlier. Her 'relaxation' had obviously not lasted very long. She went over the list three times before she was finally satisfied.

A few minutes before the princesses' expected arrival, Rainbow was told to look out for them and left the library. She soon came back with the news that the princesses' chariot was approaching and would land any moment now.

Twilight quickly took another look around the library and told the ponies - and Antonius - where they should stand to welcome the princesses.

When everyone was in position, they heard a knock at the door and Twilight opened it with her magic.
Through the door came two ponies in golden armor, probably the 'Royal Guard'. Their eyes widened as they saw the Space Marine, but they quickly pulled themselves together and announced:

"Fillies and gentlecolts, we have the pleasure to announce: Princess Celestia of Equestria, Princess of the Sun, sovereign ruler of Equestria, and Princess Luna of Equestria, Princess of the Night, sovereign co-ruler of Equestria!"

A white alicorn came through the open door, taller than Luna, wearing a golden necklace and tiara. Despite the unfavorable angle, Antonius could catch a glimpse of her cutie-mark; a sun. Her hair had several pastel-colors and flowed in an non-existent wind, just like her sister's.

She looked at the Space Marine. Her eyes widened a bit and Antonius could see a mixture of awe and worry on her face, but just for a fraction of a second, then it became a like a mask - a friendly and inoffensively smiling mask.

Great. That was the face of a versed diplomat. Antonius knew he had to be wary and look for little slips she would hopefully make to discern her true intentions.

She was followed by Luna, who walked up to her side after passing the door.

The ponies knelt down and bowed deep, Antonius made a small complementary bow.

"Antonius, kneel down!" whispered Twilight from below.

Kneel before a xeno? Never.
Antonius looked down at her and saw that she was quite nervous.

"Can't," he whispered back curtly.

"What? Why?"

Twilight started sweating. Why was she so nervous?

As Celestia showed no intention of introducing herself and seemed to be waiting for Antonius' answer, he quietly told Twilight:

"I solely kneel before my superiors of my chapter or the Emperor himself."

Twilight looked close to panic as Celestia finally spoke:

"I greet you, Antonius Varus from the Imperium of Mankind. I am Celestia, Princess of Equestria. You already know my sister, Luna.
You do not need to kneel before us, as we are only princesses of ponies and no royalty to you."

As a member of the Legiones Astartes, Antonius did not even kneel before human royalty, but explaining this would definitely go too far.
He bowed again and said:

"Thank you for your greeting, Princess Celestia of Equestria. It is a honor and a pleasure meeting you and your sister."

Diplomacy, again.

Twilight visibly relaxed now and the ponies stood up.

"First and foremost, let me thank you for saving Twilight's life back in the forest," Celestia said,
"you have proven yourself to be a true friend of ponykind."

Friend. Again. Was that the favorite word of every single pony in existence?

"Let me further thank you for helping my sister during her nightly patrol," she continued,
"you really are a great help to us."

Oh yeah. That was what he always had wanted to be.

"Thank you for your commendations, princess," Antonius answered, hoping all of this diplomacy would be dimmed down soon.

He really preferred the more casual conversation he had had with Luna last night.

Celestia nodded towards the guards and they left the library, closing the door behind them.

"Welcome to Ponyville, Princess Celestia and Princess Luna!" Twilight said,
"I thought it would be an asset to have a snack before we start the talks."

"Oh, this is great," Pinkie Pie shouted, standing next to a cloth covered... something,
"then I can show you, Antonius, the surprise I have for you!"

"Pinkie..." said Twilight, standing to Antonius' right now, obvious worry in her voice.

Pinkie drew the cloth away and Antonius looked into the barrel of some kind of cannon.
His transhuman reflexes kicked in immediately and time slowed down as he made a dive roll over Twilight to the only free spot in range.

Now, ponykind finally showed its true face.
All of the friendliness, the kindness, just distractions to make him careless.
Rarity's offer to clean his armor, just attempted sabotage.
It fitted the experiences of humanity quite well.

Damned. He had really believed that he had found the first friendly xeno-species mankind had ever encountered. He had been wrong. Every xeno was really...

"PARTY CANNON!!!" screamed Twilight while Antonius was flying over her.

Party cannon? What the hell was that supposed to be? Sounded like some sort of contraption made by cultists of Slaanesh...

According to Twilight's reaction, she thought this weapon to be harmless. A harmless cannon? A ridiculous idea, but when a species in the universe built such a peculiar thing, it would be those ponies.

Was it just a very, very strange misunderstanding?
Time was getting short. He had to decide what to do now.

After his dodge, the cannon had no chance of hitting him without first being realigned. That gave him some time. Time he would use well.
So, after completing the dive roll, he immediately grabbed his bolter, but he did not yet take aim.
His subconsciousness had already made every required calculation to destroy the cannon - and the gunner.

"JUST A PARTY CANNON!!!" Twilight shouted again,
"It's not a real weapon and completely harmless!"

Antonius quickly checked his surroundings. Everyone had a worried look on their faces, but nobody made an attempt to attack him. Now, his eyes were glued to the cannon again.

"A harmless cannon?" he asked incredulously.

"Yes," Twilight said,
"Pinkie, fire your party cannon at the door to demonstrate."

Pinkie hesitantly pulled an attached string and the cannon shot confetti and glitter towards the door.
Damned. It really was harmless.

Antonius put the bolter back to the magnetic holster on his belt and took a deep breath.

"You really should not aim those cannons at people not familiar with that particular aspect of your culture," he said.

Pinkie Pie looked down and said:

"I'm sorry. I didn't know you were so jumpy."

"Did you just call me 'jumpy'?"

"Geez, Pinkie," Rainbow whispered,
"could you perhaps say or do something that does not almost get somepony killed for a change?"

"I must concur with Mr. Varus that we still do not know each other's culture very well, which means the probability of misunderstandings is quite high," Celestia opined,
"that's why we all should be a bit careful."

Antonius could hear a bit of tension in her voice, but she still sounded friendly.

"Not shooting at each other would be a good start," Luna smiled. Probably an attempt to diffuse the situation further.

Now Pinkie stepped up to Antonius:

"I'm really, really super sorry. Can you forgive me?"

"Sure. Tell me, was that your surprise? To blast me with confetti?"

"Oh, no, si... I mean no. That was just for presentation. The real surprise is on the table next to it."

Antonius went to the cannon and took a look at said table. There was a plate with some kind of wrap.

"Food?" he asked.

"Yes, but not just any food!" Pinkie answered,
"try it, I bet you will like it!"

"Should somepony perhaps taste it first?" Rarity asked worriedly.

"That's not a good idea. It's extra-special food for Antonius and not suitable for ponies," Pinkie told her.

Antonius looked skeptically at the wraps, but finally he picked one up. He started his usual routine again by sniffing at the food, then, he took a bite. Every pony - and dragon - in the room waited for his reaction.
After swallowing, he turned to Pinkie:

"How did you achieve that?"

"You like it? Is it substantial enough?"

"The taste is superb, but even more intriguing is the fact that this wrap has about the same nutrition value as real Space Marine food. I have to ask again: How did you achieve that?"

"Oh, that's my little secret. But I can tell you, it contains meat and lots of vegetables. The batter was the most difficult part and contains the most nutrients, the filling is mainly for taste and contains the nutrients I could not stuff into the batter."

"My compliment."

That really was a surprise. Pinkie had made Space Marine food without knowing anything about Space Marines, which was actually quite impossible, yet, every implant involved told him that these wraps were perfectly safe.

"Well, I think we can turn towards the snacks now," Twilight said, clearly relieved.

Every pony - and dragon - fetched some food now. The princesses headed directly towards the cakes.

Soon, there was a lively discussion about the strange magic Twilight had spotted in the clearing.

"Antonius, do you have any idea what this feral magic could be? Have you encountered something alike ever before?" Luna asked.

"Without being a psyker, I can only make an educated guess," he answered,
"but I assume it is Warp energy."

"Warp energy?" Twilight asked,
"you used the expression 'warp' when you told us how you got here. What exactly is 'warp'?"

"The Warp is a psychic dimension parallel to real space. If you have a warp drive, you can use it to travel great distances. If you are a psyker, you can tap its energies.
But you must be aware that every interaction with the Warp is extremely dangerous. When you are not properly protected by special shields or excessive training, contacting the Warp is most likely to kill you. It can even wipe out your entire planet."

"WHAT? Why is it so dangerous?"

"It is not uninhabited. Daemons dwell there, as well as the four Gods of Chaos. Well, I think now the time has come for our talks about the history of our species, for a thorough answer to your question is closely related to the history of mankind."

Celestia nodded.

"Yes, I really would like to hear about your kin. Let's all sit down."

Everyone sat down, the princesses in front of Antonius, and Celestia continued:

"Mr. Varus, if you don't mind, we could talk about mankind first and postpone ponykind."

"Sounds reasonable."

Antonius was curios how the ponies would react to the history of the mankind. He would have to tell them a short and simplified version, of course.
He cleared his throat and started:

"In the late second millennium of our calendar, or M2 for short, mankind made its first tentative steps to the stars and started colonizing its own solar system.
Later, in M18, the warp drive was developed, and journeys of several centuries became journeys of several days. That way, humanity started expanding across the galaxy. This was the golden age of mankind and is now called the 'Dark Age of Technology'."

"I'm sorry to interrupt, Mr. Varus," Celestia said,
"but, when it was a 'golden age', why do you call it 'dark age' as well?"

"Because of the way it ended. Humanity was greedy for new technology and learned the hard way that such technology can be a two-edged sword. Furthermore, a lot of information about this age is lost, so the term 'dark' actually has two meanings."

"What happened?"

"Mankind created artificial intelligence; machines that were able to think like biological life forms. They were created to help mankind, but they eventually rebelled and almost brought mankind to ruin."

"So that is what you mean by 'two-edged sword'. I'm sorry to hear that you people had to suffer so much."

"Truth be told, that was just one of several problems mankind had to face, and it was not the most serious one.
By M22, lots of pyskers began to appear. Many of them became possessed by daemons and whole planets were overrun by the Warp filth and lost."

"So that is the reason you are not very fond of our magic."

"Correct. It is nothing short of a miracle that you are using your magic all the time without any of these negative consequences.
It would be very interesting to discover the reason for this."

"I concur. It could be very important for ponykind. But please, go on."

"Okay. To make things worse, warp storms suddenly appeared and isolated entire systems. On a lot of planets, this isolation led to anarchy and regression to barbary. Several alien races used this weakness and raided and devastated many of humanity's worlds. Other planets, like Terra, the cradle of mankind, were dependent on other planets to supply them with food. With interplanetary travel made impossible, those planets were not able to feed their population anymore and countless billions starved.
This was the end of the Dark Age of Technology and the beginning of the Age of Strife."

"Oh my goodness," Celestia said bewilderedly,
"that is incredible. A disaster of incomprehensible scale."

"Yes, it was. The few survivors were ruled by several warlords who constantly battled each other.
It stayed that way until M29. Then, the warp storms started to becalm themselves, and another warlord appeared openly for the first time. This man, an incredibly powerful psyker who had lived on Terra for several millennia and would later be known as the Emperor, saw that the time was right to reunite mankind. With diplomacy or - if necessary - war, he pacified or defeated the other warlords and founded the Imperium.

"By M30, mankind on Terra was united again, but that was just the beginning of reuniting all of humanity. The countless colonies throughout the galaxy were still on their own. The Emperor knew that he could not do this all by himself, he needed help, but not just any help. So, he used his own genes to create 20 warriors such as mankind had never seen before; the Primarchs. They were supposed to lead the armies that should liberate the colonies from alien oppression, but the gods of chaos abducted the infants and scattered them across the galaxy. The Emperor, however, knew that his sons were still alive, so he thought of a way to find them and help the human planets at the same time.

"He used the genes of his Primarchs to create gene-seeds to upgrade normal humans to warriors without peer. While inferior to the Primarchs, they were easier to create and still vastly superior to normal humans: the Space Marines; 20 legions, each created with the genetic material of a different Primarch.
With their help, the Emperor started the Great Crusade to find his lost sons and reunite all of mankind."

"Did he find his sons?" asked Fluttershy.

"Yes, he did," answered Antonius,
"all of them. They had become important leaders on the planets they had been cast on and were given command of the Space Marine Legion that had been created with their genes.
Having said this, we only have information about 18 Primarchs. The other two remain mysterious, we only know that they were found, but we have no further knowledge what happened to them.
But be that as it may, the Great Crusade continued for around two centuries under the Emperor's command, later accompanied by normal humans who formed the Imperial Army. Then, the Emperor declared His favorite son, Horus, Primarch of the XVI Legion, Warmaster and put him in charge of the Great Crusade while He traveled back to Terra."

"Something bad happened, didn't it?" asked Twilight,
"by now, it almost sounds like the beginning of a happy end, but according to what you told us earlier, there was no happy end.
You told me that you are fighting Chaos. Did they attack you?"

Antonius' voice became harder as he continued:

"'Attack' does not even start to describe it. The devious Gods of Chaos corrupted Horus and he turned against the Emperor."

Antonius noticed that Luna looked really shocked now, then, she lowered her head, as if she was ashamed of something.
He decided to ask her about that later and continued:

"Eight Primarchs and their legions joined him and they started a rebellion which is now known as the 'Horus Heresy'. They did not start open war, but used treason instead. I will give you an example of what they did:

"The XIII Legion, the Ultramarines, were of course loyal to mankind and the Emperor.
The XVII Legion, the Word Bearers, were supposed to join forces with them in a campaign against an alien threat and meet them at the Ultramarine planet Calth. But the Word Bearers had joined Chaos.
The Ultramarines did not know this and welcomed them as friends, as brothers. They did not even know yet that there was a rebellion at all.
The traitors pretended to be friends and brought their ships and troops into position, then, without warning, they started slaughtering the Ultramarines and other loyal forces on and above Calth. Within a few hours, more than 100,000 Ultramarines, millions of soldiers of the Imperial Army and countless civilians were killed, murdered.
The remaining Ultramarines and other loyal forces managed to regroup and finally repulse the Word Bearers, but not before the Chaos scum had managed to poison Calth's sun."

"THEY DID WHAT?" shouted Celestia.

Antonius had noticed that her mask had started to crumble while he had told about the Horus Heresy, now she was utterly shocked.

"They fired at Calth's sun in an attempt to create a nova.
Although the Ultramarines were able to foil this plan, the sun had already taken damage and its radiation had become lethal. The survivors of the battle had to flee into the underground caverns of Calth to stay alive."

"The wickedness of those Word Bearers is simply unbelievable."

"Yes, it is. Even revered Roboute Guilliman, Primarch of the Ultramarines, was shocked. It was not their last atrocity, however:
They also created a warp storm to prevent the Ultramarines from helping the rest of mankind and Terra.

"After setting half the galaxy on fire, the traitors finally launched their attack on Terra 014M31. Horus himself was leading the assault onboard his flagship.
The Ultramarines meanwhile had managed to set forth for Terra, but they had not arrived yet.

"So, while the loyal Space Marines and the traitorous Chaos Space Marines fought on the surface of burning Terra, the Emperor teleported onto Horus' ship, accompanied by two of his sons, Sanguinius, Primarch of the IX Legion, the Blood Angels, and Rogal Dorn, Primarch of the VII Legion, the Imperial Fists, as well as a number of Space Marines and Custodes, the Emperor's own bodyguards. Unfortunately, they were scattered through the ship, and they had to fight their way to find each other and the traitor Horus.
Sanguinius found him first. He was able to damage Horus' armor, but was slain by him.

"The Emperor found them, Horus standing over Sanguinius' dead body, and battled his former favorite son. It was a long and grueling duel:
the Emperor, a psyker of unparalleled might and Horus, a creature imbued with the energies all four Chaos Gods; the Emperor could have won, but he still felt mercy for his son and could not bring himself to kill the traitor. Horus used this moment of weakness and lethally wounded his father.
Meanwhile, one of the Emperor's companions had found his way to the bridge and immediately attacked Horus. The traitor just laughed and blasted him apart with his dark powers.

"Now, the Emperor finally realized that he had no other choice than to kill his son, lashed out at him with his full psychic power and killed him.
Horus was dead, abandoned by the traitorous chaos gods, but the Emperor was barely alive, either.
He was found by Rogal Dorn and only had enough strength to demand to be taken to the Golden Throne, an arcane machine that was capable of sustaining his last bit of life.

"There He still sits today, for more than 10,000 years, kept alive by ancient technology and the sheer force of His own will, a living soul bound to a dead body, and watches over mankind. One thousand psykers give their lives every day so that He may live.
He directs the Astronomican, so that our ships can navigate the Warp.
His soul roams the Warp and relentlessly keeps the Chaos Gods at bay.
He is our guidance and the reason that mankind has not been wiped out yet.
He was, is, and will always be, the Emperor of mankind."

After a short pause Antonius continued:

"After the Battle of Terra, the loyal forces were able to repulse the Chaos forces into the Eye of Terror, a region where the Warp bleeds into real space.
The legions were split up into chapters to adapt to the new situation; an attempt to pacify the galaxy had become a struggle for survival.

"Now, we have the year 039M42. Up to today, we fight the traitors that joined Chaos, the daemons of the Warp, hostile aliens and every other threat that endangers mankind. And we will continue to do so until we are not needed anymore, no matter how long that will take."

Antonius had been keeping an eye on the ponies during his story. They had showed great empathy and now, they looked truly upset.
Celestia swallowed hard and said finally:

"I really don't know what to say. I never imagined that something like this could happen, it is a few orders of magnitude worse than the worst I could think of. Your species had to suffer so much... yet, you endured.
We want to help you, but I don't know if we can. The universe should be a place of peace and harmony, not a place of unending battles."

"Forget your ideas of peace and harmony amongst the stars, for those times are long forgotten.
In the dark times we are living in, there is only war, the screams of the innocent, and the mad laughter of bloodthirsty gods."

Celestia looked in Antonius eyes. He could see sadness, but also determination.

"No," she said,
"that can't be everything. The universe can't be that cruel."

"The universe itself is not really cruel, just uncaring. It follows a simple rule: Either you learn to kill, or it teaches you to die."

"Even if that is true, there must at least be a way to change that.
But we are not used to that kind of problems. We are just ponies, we don't have a great empire that can influence the whole galaxy."

"Hey!" Rainbow Dash shouted,
"but we have the Elements of Harmony! They worked against Nightmare Moon and Discord!
I bet we could use them to blast some Chaos flanks!"

Antonius silently thanked the Emperor for the enthusiasm of this mare. Now, the Elements of Harmony were on the table.

Celestia looked at her, deep in thoughts.

"I'm not sure of this. The Chaos mankind has to face is far worse than anything Discord has ever done. I don't know if the Elements will work at all. Furthermore, you six, as the embodiments of the Elements, are needed to use them, so you would have to accompany Mr. Varus back to the Imperium."

"I'm sorry to interrupt," Antonius said,
"but what do you mean by 'embodiment of the Elements'?"

"Each Element of Harmony needs a bearer, a pony who is the embodiment of the Element, who represents it.
Fluttershy's Element is Kindness,
Pinkie Pie's is Laughter,
Rarity's is Generosity,
Applejack's is Honesty,
Rainbow Dash's is Loyalty and
Twilight's is Magic.
Without them, the Elements of Harmony are useless," Celestia explained.

Oh, that was interesting: Exactly these six ponies were needed to use those Elements.

"But you are right, Rainbow Dash. We have at least a chance to help mankind," Celestia continued.

Huh? Success? That easy? Well, Antonius had expected more complications.

"But there is one thing I have to ask you first, Mr. Varus..." Celestia continued.

Aha. There was the catch.

"...tell me, after all of this negative experience with other species, how will your Imperium react to us?"

Oh. THAT was quite a catch.

"I will be honest with you. If a standard exploration vessel had found you, things would probably not have gone peacefully.
But I have found you. When I report back to my chapter, they will listen to me and not hurt you."

At least if he could explain everything without getting executed... nah, they would certainly let him finish speaking and see his reasons.

Antonius continued:

"And as you are willing to join our fight against Chaos, we will not only welcome you, but also protect you."

"Are you sure about this? You must understand that as a princess, it is my duty to protect my subjects."

"Quite sure. Our Chapter Master, Marneus Augustus Calgar, is a reasonable man. Furthermore, we already have worked with aliens to fight common threats."

Celestia nodded, her mask intact again.

"Sounds good, but this decision must not be rushed. We are talking about jumping into a war of unimaginable magnitude, after all."

So, no success yet, but probably already on the road towards success. The ponies were friendly, but careful.

Antonius nodded towards the princess and said:

"A reasonable decision. Now I have to ask a question:
I have already heard about Discord, but Rainbow Dash also mentioned a 'Nightmare Moon'. Who, or what, is that?"

Celestia looked sad now, and Luna looked ashamed again. First Horus, now Nightmare moon. Was there a similarity? What was the secret behind all of this?

"Well," Celestia began,
"I guess it is time to tell you the history of ponykind."

So Celestia told Antonius about her species, giving him a quick overview of pony history.
She started with the unification of the pony tribes and the founding of Equestria and continued with the reign of Discord and how her sister and she turned him into stone.
Antonius already knew that the Elements of Harmony could petrify a Chaos daemon, but it was interesting to hear the full story.
According to his fondness of changing things - in appearance as well as in behavior - Discord was obviously a daemon of Tzeentch, but an unusual one. He was content with making childish or at worst cruel jokes, he did not even kill a single pony; that was rather harmless for a Chaos daemon.

Then, Celestia told him - a bit reluctantly - about Nightmare Moon, and Antonius finally understood Luna's reaction to Horus.
They both were traitors, corrupted by daemonic powers - this 'nightmare' was probably some kind of Chaos force, perhaps also a spawn of Tzeentch.
They both spat on their duties and tried to destroy their older relatives to become rulers of their kin, not caring what they did to the population.

The Nightmare Moon story was almost like a less grim version of the Horus Heresy, as it happened on a much smaller scale and Celestia had been able to stop Nightmare Moon.
Furthermore, Antonius got to know a second ability of the Elements: Banishing foes.
So, why was Luna sitting here? Antonius was curious to hear the rest of the story.

Twilight took over and continued with Nightmare Moon's second attempt to seize power, this time foiled by her and her friends by using the Elements of Harmony again. But now, their effect was completely different.

Antonius could hardly believe it: These Elements could not only petrify daemons and banish foes, they could also perform some kind of instant exorcism?
That was... unbelievable!
The Elements of Harmony could be the most powerful and useful relics mankind had ever encountered!
What would happen if you used them against a Chaos Space Marine? Or even a Chaos Primarch? Petrification? Exorcism?

Well, after all these traitors had done, Antonius would honestly prefer a more... final solution than that, something like obliteration, extermination or annihilation.

Despite his personal feelings, he knew that the Elements of Harmony were probably the ultimate anti-Chaos-weapon. And mankind needed the ponies to wield them.

Antonius had to stop his train of thoughts as Twilight continued the history lesson - she really seemed to like it - with Discord's second appearance and subsequent defeat, which also reverted everything he had changed while being active.
A forth power of the Elements.

Antonius decided to extend his mission: He not only had to return to his chapter, he also had to befriend the ponies and thus acquire the power of the Elements of Harmony for mankind!

For the Emperor!