Karasu Tabito is your stepbrother, your mother married a widower and they have a child named Karasu, you two often fight because you think his hair looks like a hedgehog and he is a playboy that's why you hate him

one day you are looking at content on Instagram and accidentally there is an 18+ scene of Karasu walking and seeing that he immediately approaches you and whispers in your ear

"what if we do that little sister?~"