Yeah I am all for the older sister finding out and then having aggressive revenge sex with Katsuta, and then she screams out the classic line, "well am I better then my sister"?
Maybe Chiyo is watching from the crack in the door, and maybe she decides to join in, who can say?
"Doing it with my girlfriend's sister feels so wrong"
And yet here you are, doing it again.
I kind of want another chapter where maybe the sister finds out and then it somehow leads to a 3P, or something.
Plot twist: her sister isn't his girlfriend, they made that up in order to hook her up with the boy so that the sister can date boys in peace without having to worry about her stealing them away...
Maybe Chiyo is watching from the crack in the door, and maybe she decides to join in, who can say?