Help with finding a manga

[Ark-]

I've been trying to find a certain manga, the story revolves around a boy and his little sister that has been turned into a kaijuu due to his father, the big brother are capable of becoming a kaijuu himself and can revert it, in order to return his little sister into a normal human again, he has to fight a remnant of his late father experiment, i remember that it isn't too long, also, there's another character that i remember that became MC (big brother) maid/lover, there's also another character that is a kaijuu maniac,

 

[Reiru]

@Ark- https://mangadex.org/title/11541/kiriwo-terrible unfortunately you need to read this in other site