The arts great but the concept is awful, it's from the perspective of a guy who looks big but sucks at fighting and its secretly his sister who is the great fighter, this identical concept of secretly weak character has been done before, Hercule, King, but those are side characters.
This could have worked if there was some sense that the MC wanted to improve himself, but it seems to be all about the sister getting stronger. I'm sure some will enjoy it but I don't see the appeal of a series that follows a weak guy constantly complaining about how weak he is while watching a bunch of guys trying to fuck his sister.