Princess Aurora

The door unlocked, getting both ponies attention.

"Princess Celestia!"

"Hey mum."

"Good to see you are both safe and sound."

"Princess, I still don't understand. Why is Rainbows magic so dangerous and why am I here too?"

"We will explain you more in time. But first: Aurora!"
Dash stood up.

"Come with me. You need to get back to your training."

Dash grunted. Celestia went out of the room. Before Dash left too, she gave Twilight a sign to follow her.
The three ponies were in a big hall underneath the castle, a place no pony except the royal family knew. Twilight was stunned that they even Had another room, in the ground.
Celestia brought a little bunny in and placed it into a freedom-cage that would normally be used in a garden. A few meters away from it was a normal cage. Both were opened.

Celestia nodded to Dash. Twilight stood next to Celestia, eager to watch whatever was going to happen.
Dash walked over to the bunny. She took a deep breath and relaxed. Then she stared the bunny in the eyes. They were practically glued to each other.
Twilight had no idea what they were doing.
Dash began to close her eyes, her face completely in concentration. The bunny was still frozen like in stone and stared at Dash with his ears straight to Dash. The Pegasus began groaning from the effort.

Now Twilight got concerned.

Dash began to glow lightly in a full rainbows colors. Her legs became shaky. With a last grunt, more a deep sigh, she finally collapsed to the ground.

"Rainbow!"
Twilight ran over to her. She helped the panting Pegasus to her haunches. Then their attention went to the bunny, that was hopping straight into the cage, still having this blank stare like Dash and it were still staring into each other's eyes. Once it was in, it turned back to face Rainbow. Then it got his normal bunny face back and began preening itself.
Celestia closed the cage and nodded to Rainbow.

"Not bad, the first try after years of no training, Aurora."

"Thanks"
Dash said weakly, still panting.

"Maybe you should get some rest. Can you stand?"
Dash tried to get up. Still shaking she managed to walk out off the room with Twilight by her side.
They went back into Rainbows room. Dash's shivering grew worse. Twilight and Rainbow laid on the bed, Twilight wrapping the shivering Pegasus into the blanket.

"Rainbow? Are you okey?"

"Yeah, I'm good."

"You don't sound so cold, but you're shivering like you were freezing."

"I'm not cold. Well, I'm not feeling cold."
She said, rubbing her hooves together. Twilight got curious and touched one of Dashs hooves. She shrieked back in not even a second.

"Wah! Dash your hooves are ice cold!"

"Well, do you know now why I don't let Anypony touch my hooves?"
Twilight nodded. The throbbing feeling in Dash's stomach made her groan again and she turned to her side.

"What's wrong? Does anything hurt?"

"Well, it's not really 'pain'. I just hate that feeling."
She placed a hoof over the place on her stomach. It was getting moved up and down by the pulsing. Twilight raised an eyebrow. Then moved a hoof to touch it too, but Dash moved it away.

"I don't think you would like that. Either you would get the creeps or have to throw up."

"What? Why?"
Dash rolled her eyes. She sighed and grabbed Twilights hoof. Twilight slightly jumping from the cold touch. Dash placed her hoof over her stomach. Twilights eyes widened. It felt like Dashs heart would be in her stomach, without anything covering it. Only that it was more like a ball. The more pressure she put onto it, the more her hoof was moved by the pulsing.
Dash was just looking at her like it was nothing.

"Twilight."

The alicorn was still frozen.

"Twilight!"

No reaction.

"TWILIGHT!!"

She shoved the hoof from her stomach. Twilight finally snapping out.

"Twilight, you can't tell Anypony about this. This is TOP SECRET."
Twilight nodded, then she passed out.
Dash sighed and wrapped her blanket around the alicorn, snuggling up to her until the shivering finally left.