There is no way in Hell Rokurou managed to learn/remember anything he studied that day. How could he? So much happened, so many things to think about, and Debby was tied up on his bed waiting for him to play with her.
I think this might have awakened something in the two of them. Also it’s fucking adorable the way Debby’s body just moves on its own, her wings and tail wagging alone are cute enough, but the way the eyes on her head move and act makes it all the better.
Debby really knows how to tie herself provocatively doesn’t she?