Six years after his best friend disappeared, Sei meets an older man in the hospital who wants to give him his inheritance. And the older man's grandson, who has refused his money, is a very changed version of Sei's friend from six years earlier.
There is a dubcon scene (I think it's fair to say it's noncon) between the two main characters, although it works within the context of the story, since the goal was to frighten Sei into leaving him alone. He was trying to be cruel.
Ano Koi no Tsuzuki