This has come up several times, and the answer is still the same: Sugu is so far gone that she wants her big brother regardless of what he does, hell, in previous updates she even said that she would 'respect his decision no matter what'...while at the same time unable to resist forcing herself on him to get a taste of his dick, and she DID react positively to him trying to take the initiative in the bath XD Regardless of if Kirito became a scumbag, she would still want him (And realistically he never would be as bad as Hebishima was, lmao, reminder he even drugged and blackmailed like a hundred girls in total, and it was implied that when he got tired of them he moved on usually after making them sell their bodies for his sake...as bad as Gigachad Kirito may be, he's only targetting the girls close to him that were basically throwing themselves at him anyway, so yeah XP).