He called it regeneration.

He gave her instructions.

“Just watch over me, Derpy. I’ll need a day or so to feel better. It all be alright, just make sure the TARDIS keeps and stays on autopilot. You remember what autopilot is?”

“Yeah it’s when it flies by itself. But I still don’t understand.” She asked him.

“Well, it’s a bit complicated. I don’t know how it works this time with the equine physiology, I’ve been human every time I’ve done it before. I think I’ve gone down to just one heart when I came to your world, I think it was like a half generation. But this... Well, it’s kind of a bit of mystery for meself... but I know I’m in good hands- err hooves.”

And that was all she had to do. Just watch him.

If anypony told her a year ago that they wanted to help her with flying she would have taken it in a heartbeat, she being a pegasus. But that was before she met him, the Doctor. His flying machine, TARDIS he called it, was a blue box that had buttons, switches, and knobs on the inside of it. Derpy haven’t had the slightest idea how it worked.

“Don’t be worried. Autopilot!” He said comfortingly pointing a hoof to the control panel. “It flies itself! Just sit back and catch up on some reading or something, and when I come back I’ll be right as rain.”

“Are you going to be OK?” She sadly asked stepping closer to him.

“You know I hate it when you frown,” He stepped closer and placed a hoof to her cheek. “I’ve told you that before.”

She did remember.

“Your wings won’t work in space.”

It was what he told her once on their first trip.

“There is no atmosphere or gravity in which you can create an airfoil to gain the lift to get off the ground. Well there is no ground really.”

“No ground?” She asked. “So you would just keep falling and have nowhere to land?”

He laughed. Which was kind of opposite to what Derpy was feeling at the moment, she felt horrified.

“You’re frowning. I hate it when I make someone frown! Come on, this is an adventure, let’s find something to get you smiling!”

“You’re still frowning.” His words brought her back from her memory to the present.

Derpy shook her head, getting lost in her thoughts was somewhat of a flaw of hers, along with other things.

“Listen,” he said stepping forward and placing his forehead against hers. “I’m a little scared too. But I feel more excited than scared. The last time I had done this was because of an accident or something bad happening. But this time... I dunno I think, NO! I just know that something with is going to make this special. And well, I have you.”

She reached up and kissed him on the cheek.

He smiled.

“You're not the first person to kiss me. But after traveling around, and seeing so many things. Normally it’s been me asking for others to join me by their side. But this time it’s the other way around! I want to be by your side. I know, isn’t it weird?”

He looked deeply at her. He wanted to kiss her back, she could see it in his eyes. But she could see something hold him back.

“Selective voluntary regeneration!” He said immediately pulling away from her. “It will be taking a step away from being who I am now, and become someone who I want to be. Someone who can...”

He leaned back in closer to her face looking like he was going to kiss her again, but stopped halfway. Derpy finished the job, leaning forward and kissing him.

She pulled away, and he looked back with a somewhat intrigued look on his face.

“Yes that,” he said with a nod. “The pony I change into on the outside may still look like what I do now, but emotionally, and physically on the inside I will be...”

He stopped again, struggling with his words.

Derpy place a hoof to his lips.

“Just, tell me why you’re doing it?” Derpy asked.

“Well isn’t it obvious,” he said cocking his head to the side. “For you of course.”

That was all she had to hear.

“OK,” he said suddenly gasping as he was leaning against the console. “It’s coming! Very soon now.”

He reached a hoof up and turned a few knobs.

“Autopilot engaged. And the rest is just waiting.”

“Doctor, you don’t look good.” She said to him

“It’s alright.” He said waving a hoof, taking another pained breath. “All part of the transformation process. This happened last time.”

There was a loud bang, it came from the side of the TARDIS and it rocked to the side.

“What was that?” She asked.

“I dunno,” he said in a labored breath.

He ran over to the other side of the console, and hit a few buttons.

“What!? Impossible!” He said looking a the little screen and blinking buttons.

“What?” Derpy said, dashing up next to him.

“The sun! Your sun, is moving.”

“What do you mean?” She asked.

“Planets and bodies around in a single star system orbit around that star. That’s how gravity works.”

There was that word again: Gravity. The thing that makes ponies fall.

“But the TARDIS is telling me that the shift in gravity is because your sun is moving!” He said staring perplexed at the screen. He then let out another groan.

He hit the ground looking like he was sick.

“Doctor!” Derpy screamed.

His eyes started to glow.

“DOCTOR!”

“It’s happening. Right now!” He said, and then his whole body erupted with light.

The TARDIS gave another shake.

Both Derpy and the Doctor were thrown to the opposite side of the room.

She flapped her wings, and caught the Doctor, cushioning him from the sudden impact of hitting the wall.

He was still glowing. not a brightly as before, but sparkling like stardust or magic. His eyes were closed.

“Doctor? Can you hear me?” She called to him.

He gave no response. He told her that would happen once it started. The clock had now started, he will not wake up for a day now.

“Doctor I don’t know what to do.” She said holding on to him. “Oh Celestia help us!”

She buried her face into his chest.

The room shook again harder this time. Sparks flew up from the console.

She looked at his still glowing face. He looked so peaceful. He was changing for her. That’s what he said. She brushed his mane with her hoof.

There was another boom and a crash.

“Oh Celestia, Luna! Help us!” Derpy sobbed.

She looked over at the console. Her mind remembering that the Doctor told her the autopilot would take care of everything.

“DO SOMETHING!” She screamed at it.

A loud click came from the console and Derpy heard the familiar churning the TARDIS made whenever it disappeared to another time.

She did not let go of him when the pistons moved and buttons flashed.

“It’s working,” she said. “It’s getting us out of here.”

But something was wrong.

She saw the console starting to fade away, the walls too, and the floor.

The TARDIS was leaving, but they were staying put. It was leaving without them.

“Noooooooooo!” She cried as the room disappeared to a black abyss of space.

She instinctually flapped her wings.

Your wings won’t work in space.

Nothing happened, she felt weightless

So you would just keep falling and have nowhere to land?

That’s what was happening. They were falling with nowhere to land. Falling across the universe.

“I’m sorry,” she cried to him. He still unconscious, and glowing like a shooting star.

“I’m sorry!” She said again.