"So… I had this really weird thought," Amy said.
"Uh oh," Victoria replied. "That's usually a bad sign."
"Yeah, probably," Amy agreed. "I… didn't get much sleep last night, that could be why."
She yawned. "But, anyway, uh… I suddenly thought. If I lost a finger, would I still be me?"
"…yeah," Victoria said. "Are you okay, Ames? You sound like you're about to fall asleep into your lunch."
"You're not wrong," Amy said, distinctively, and yawned again. "But it's a really weird idea, so maybe I need to be like this to think of something so bizarre."
She shrugged. "I mean, uh… who am I?"
"...you're my sister," Victoria said, tentatively. "Is this a trick question?"
"Not a trick question," Amy replied. "But it's because I had that thought about the finger."
This time, the yawn was much bigger than before.
"Mrf," Amy said. "Anyway. Anyway, uh, it doesn't have to be a finger. The point is, the finger is fungible – the point is, I've healed people with pretty bad injuries before, but not brains. Not myself."
She tilted her head. "But, what's really me?"
"...hold on, hold on," Victoria said. "Ames? Don't do power experimentation while you're low on sleep, okay?"
It wasn't very clear if Amy had heard her and ignored her, or just not heard her at all.
"The bit that's me is my brain," Amy said, distinctively. "Everything else is sort of… extra. Important extra, but extra."
"So… uh," she added, did something with her power, then fell onto her plate and began snoring.
Five minutes later, a teacher arrived.
"All right, what happened… here?" he said.
Then stared.
"Uh," Victoria began. "So… as far as I can tell, my sister got very tired, had a weird realization about her Manton limitation, then cured herself of not being a cat girl and fell asleep."
Amy made a mumbling noise.
"She… might be asleep for a long time," Victoria added. "I should probably take her home and put her in a sunbeam or something."
AN:
Like Amy, I was low on sleep when I came up with this one.
Shaper probably took what it could get, though.