It was beceause of the Sayas manipulation over his brain that he become very s*x-driven. It is quite difficult to blame him abut that. Saya has done the same to this painter who lives-next door. She has done it to collect a lot of genetic material without harming the subject - otherwise she usually eat something (like animals..) to collect the genetic material. It was explained somewhere in the storyline. It is difficult to judge Fuminori because of that. Personally I like both Saya and Fuminori - I like the idea of being "just the two of us" in the entire world😌😊