THEORY

So boom.
Rui has always liked Shion but never said anything bc he felt like shion would deny him. When shion first turned into a girl rui said he was exactly his type (in a girl form) and I think he meant he liked that there was a girl exactly like shion. Also rui never seems stressed or anxious about doing stuff with shion (even fingering him even when shion was a guy lol) and not to mention rui Alr knew about how guys could have orgasms in their ass meaning he’s definitely looked into it before. I think rui has always liked shion and shion turning into a girl was just an excuse rui used to finally be with him romantically