@makc123 This whole mess was all premeditated in the first place. Kei knew he was going to leave to Tokyo with his parents and liked Yo from the beginning, so what he did do in the end?
Kei knew Yo liked Mitani, so he pulled that stunt on him (playing with Mitani's feelings and kissing her) to make sure that Yo and Mitani would not progress at all while he was gone. And it worked; for three years, the relationship between Yo and Mitani crumbled and they stopped talking to each other.
Just enough time for Kei to transform and come back to convert Yo into accepting his femboy ass. The lesson? Don't fuck with traps, they'll play you like a clown.