since blood related incest rarely happens in anime/manga (the other manga is exception for some reason), and I already can see that the imouto is the winning girl based on chapter 0
Man, this is the kind of shit I was talking about with Mao from the last chapter, lol. She throws her very real feelings out there and when Keiki sounds like it would be something he'd be very open to, she throws out that stupid "Just kidding!" shit and then we're right back where we started, hahahaha.
Is this just me or manga artist is making sister's breasts bigger when she have a cozy moment with the MC? Also obviously nipples are getting hard. We saw it in previus chapters as well.
I don't remember reading about her erected nipples in LN.