Welp, after getting up to day with the manga, I can finally say that this series suuucks really bad (not to shame the scanlators involved, the work is amazing), but damm this manga is full of insufferable characters (the sister) and the cliche humor of the MC getting punched by the girls around.
I will continue the series tho', since I wanna see how it ends.
PD: I don't like NTR, but the sister deserves to suffer from it to the core.