After Queen Chrysalis and her Changling army has been defeated, peace across Equestria has returned, thanks to Princess Twilight Sparkle and her friends, Princess Cadence and her husband and Twilight's brother, Shining Armor, in using the power of love and friendship against the Changling queen. Now Equestria is free from the Changlings, and now they continue to live in stability.

But ever since Celestia was blamed for all the crisis with the Changlings, Grun, adopted son of Princess Cadence and Shining Armor, vows to get revenge against Celestia.

Since having a troubled childhood, he tries to managed everything he can, and tries to succeed. But after the Changling empire and their queen has been defeated, his family later became sick. And Celestia tries to help his family. But as couple days passed, they passed away, saddened Grun. And he was adopted to Shining Armor and Cadence afterwards, and became an adopted brother to their daughter, Princess Flurry Heart.

But as time went, he blames Celestia for not helping his sicken family, and calls her a "coward", for not defending her kingdom before they were too late, vows to avenge his family. He also has strong hatred towards those who bullied him, and refuse to forgive them, vowing to kill every single one of them. He swore to make Celestia know how she would feel if he would take her sister, Princess Luna, and marry her. Grun truly loves Luna, and adores her night. And he vows to marry her if he wants too. However, Celestia welcomes the relationship of him and Luna, by Grun`s luck, but still refuses to show forgiveness.

Soon he thought of his ideals; creating a new government in Equestria that would be ruled with a better protection from future threats, a change of the nation shall be no longer neutral, and would make a better and stronger military and form an alliance with a military willing to fight future wars.

During his birthday, commanding officer of Equestrian military, General Skyline; also Grun`s former JROTC teacher, was invited by Cadence, in dismay of Grun. But as he first time seen his former teacher that he despises so much, he immediately had a thought, realizing that if he murders Skyline and frame somepony, he would had an opportunity to assume command of the Equestrian military itself, and would start his own coup de taut force.

He also remembers that General Skyline`s allergic to pin ink if he gulps it, and would probably die. He then finds a glass of punch, and finds pin ink to use it to disguises it as grape juice. Before he gives the drink to Skyline, he waits for Cadence and Shining Armor to walk away and goes on to talk with Celestia and Luna. As he gives Skyline the grape juice, he then assures him that 'You`re relieved from your command, motherbucker.', causing him to wonder why he said it as he walks away.

So after Skyline gulps down the drink, he suddenly felt pale, and started to cough out blood mixed in the punch he gulped. Realizing that it was ink in the drink, he tries to call for help, but can`t speak caused by the drink. He then fell to the floor, catching The attention of Grun himself, who acts that he's concerned and called for help. He then checks for pulse on Skyline`s neck, and felt nothing. Shining Armor and Cadence asks Grun what happened to Skyline, and Grun that somepony poisoned Skyline`s drink, and said that Skyline`s dead. Grun then points out the bully of his, now just a friend(not interested of his friendship): Hopper. As Hopper was arrested for the crime he didn't commit, he tries to be reasonable that he didn't do it, but nopony listens.

After the death of Skyline and arrest of Hopper, Grun calls himself to be named General of the Equestrian Military, which Celestia decides to let him be who he wants, despite he`s a prince and adopted to Shining Armor and Cadence.

As Grun assumes power as a new General of the Equestrian military, he then goes out to a space colony, Side 8; which it was ruled by former state of the military might, Principality of Zeon. He then came across with Zeon`s former commanding officer, now a politician, and makes a deal that could ended up causing Principality of Zeon to be rebuild, and now becomes powerful with new weapons (Mobile Suits, nuclear weapons, and space and surface warships), thanks to Grun`s support.

As Zeon rises to power with stronger technology and advanced weapons; from the help of Grun, Zeon took control of Earth with force, and then made an alliance with Grun`s military coup. Afterwards, Zeon came to Equestrian planet, and conquers Saddle Arabia, Zebraland, and Dragon Empire! This was marked the beginning of the Galaxy Conflict(Zeon and Equestrian War).

After Grun returns to Equestria, he and Luna were on the date together. As they had a conversation that involves of what's happening to Saddle Arabia and other nations were occupied by an unknown force, Grun brushes it off and changes the subject. But Luna still felt concerned of what's happening, and Grun then insisted 'It`s none our business, let those countries handle it themselves.' So Luna and Grun walks our of the restaurant and tries not to get into an argument. But as they got clear so no pony`s watching, Grun slaps Luna on the face and pins against the wall, and gives his remarks to her.

He then states, "When I said it's none of our business, it's not our problem!" Luna then realizes that he's hiding something, but Grun reveals that he's responsible to form an alliance with Zeon military might, and they got those nations under their control, and admits that he made the deal with them. To her shock, Luna realizes that he's going rogue, and he threatens to kill Celestia if she opens her mouth about this. And Grun also said, "And I want to marry you without her blessings! If you refuse this marriage, you value Celestia`s life!" She then understands that his anger was towards to her sister, which he blames for the death of his beloved family and didn't do enough to protect Equestria from the Changlings since then. So, she forcefully accepts to marry him, and would be silent. To Grun`s delight, he and Luna would share a kiss, as it marks the beginning of their relationship, which it wasn`t official because of Grun is now a rogue and vengeful general that would care nothing but extend violence for his ideals on what he believes in.

While Celestia, Twilight Sparkle, and Cadence didn't know, Luna and Grun gotten married, and Grun never felt such desire of lust to his wife, as he also never felt such satisfaction. But for Luna, which she was forced to keep herself silent by Grun, she felt concerned of; not only Equestria, but the planet itself. Which it would be warzone, and Grun will do whatever he can to fight against those he opposes. Grun, becoming a psychopathic rogue commander, vows to fight for his own image of a peaceful era: with the help of Principality of Zeon.