He gives her a trigger

Yu decided he would give Rise a trigger phrase so he could play with her.

"Rise, I want you to make the noise of the first animal that you think of, and when I wake you and any time I and only I say embrace your inner animal, you will become that animal."

Rise puffed out her cheeks, then let out a loud, hearty "RRRRIIIIIBBBBIIIITTT!"

Yu snickered. "A frog, then? Geez, must've been really into that...oh! and if I say 'immobile idol', you will fall back into this trance. Now, wake and forget seeing Somnus."

Rise shook her head and woke up. "So, Senpai," she said, blushing slightly. "Why'd you invite me to your room, huh?"

"I just wanted you to...embrace you inner animal," said Yu.

Rise's eyes crossed, she knelt to the floor on all fours, and began to hop around the room.

"RIBBBIT!" she cried, loudly. Yu was so glad Nanako and Dojima weren't home...

A fly buzzed past Rise's face, and she stuck her tongue out to try and catch it. Yu laughed at that display.