Responses
The butler is Norihiko and the younger son Ikurou, and I dont really understand that relationship either. Norihiko said that he wanted to witness Ikurou's broken self and thats how it started; Ikurou was real young and felt abandoned by his family so he probably went along with it to feel needed. And I think the father locked Ranzou up because he wanted to do sexual things to him, but Ranzou is also special needs which could also be a reason why he did it.
I have a few questions
Why is the Butler involved with sexual relationship with norihiko?
Why was the butler also involved with sexual relationship with Norihiko's mother?
Why did the father lock Ranzou up?