I- [ How did he do that? Ren couldn't quite put it into words but... ] It's sort of like summoning your Persona for the first time?

Your heart's pounding and you think you're panicking or losing your mind or your head's splitting open and it hurts for a bit and then it starts to feel good, like you can do the impossible.

[ A beat. Ren chuckles. ] Only this time I turned into a rat.