You're a student at Hogwarts School of Witchcraft and Wizardry. You're currently sat in a transfiguration class, at the back of the room, though you aren't paying the actual lesson any mind. Rather, your attention is on one student in particular. Hermione Granger sits in the front row, upright and attentive; adorable. Everything else is a blur, a murmur. That is until your teacher, Professor McGonagall, instructs you all to pair up.
Chairs start shifting noisily and students shuffle about the room. Naturally, your attention is still partially on Hermione. You notice that she remains seated, twiddling her thumbs. Without a second thought, you squeeze your way through the shifting maze of students and arrive at her side. "Wou-- would you like to pair up?" Shit, the nerves are already taking over. You can practically feel a bead of sweat slide down your temple; hopefully she doesn't notice.
"You want to pair up with me? Uhm, yeah, sure." She replies. You're in. You take a seat at the desk beside hers. "Would you mind if I'm the caster and you're the subject?" Hermione asks. You're immediately taken aback as you hadn't been paying attention to the class, but it's Hermione asking and you'd do anything for her. Whatever it is, you're game. "If that's what you want," you reply. She smiles. Smooth.
Hermione turns her attention to her textbook and slides her finger down to a particular point, picking up her wand with her other hand. "So... Redu-- Reducio!" You squint your eyes as she swizzles her wand at you, but nothing happens. "Umm.." you ponder aloud. "I don't feel any different," you admit. "That was a prefatory spell, for your clothes." Hermione goes back to the book. "Now... Reducio Persona!" and she once again twirls her wand your way.
Once again, it doesn't seem like it worked... at first. However, once your view lowers to a certain point, you realise that you're shrinking. "Whoa..." you involuntarily eep. At first, it's kind of cool but then it keeps going. Hermione just watches on with a snicker; at least you're making her happy. Shorter than a few feet, then shorter than a metre; it finally rounds out at around four inches. Now a little toy-sized boy is sat in the centre of the desk stool.
Everything is enormous, including the girl you were ogling from afar just a few minutes ago. Her cute, freckled face is now massive, and intimidating — bearing down on you.