TIME TO GO FUCK SHIT UP, KUDOU!!
The little sister's childhood may have been pretty rough too but jesus christ, that does not give her the right to grow up into an entitled shitty brat and keep trying to get in the way of MC's blissful marriage?!
Cue flashback to the very beginning of the series and the reason why Kayden was forced to transfer his soul(?) into a cat's body in the first place O.O