Because it is Oshimi, it gets increasingly intense between all the main characters, to the point of madness. Mitani is manipulative, as is the girl from Flowers of Evil, and the mom in Blood on the Tracks, so it seems increasingly horrific, like a train wreck of emotions/desires/acts. but really all of them--Yo, Kei, and now a fourth person, Ren--all are intensely exploring what they are to each other while "using" each other in certain ways.
A continuing element of this series is an afterword at the end of each volume where Oshimi talks about his own messed upo sexual awakening that also still seems like he is lost in the dark. This is NOT to my mind meant in any sense to be "erotica," as no one seems to be enjoying all this exploration across and within genders. I should mention that Oshimi continues to be a great artist in this series, conveying all the beauty and anguish of the story. But for some readers, it might all be too graphic. But it does feel like it conveys the overwrought e