This ain't family trauma anymore. The "sister" is just a sexual harasser. It's kind of funny but also excessive at some point.
The "parents" thing is getting way out of hand. Japanese manga publisher/author, ya have to have some basic moral standards. Like holy f**k 0_0
Legit, reading this is going from 'wierd but kinda funny' to just plain bad. Imagine you're moving away from home to get an education, and when you get there your options are 'roleplay with sexual undertones', 'be homeless', or 'move back to your actual home' which she must have had some reason to leave in the first place.
And then, when you resign yourself to this game, your landlord fills your room with pornography, constantly insinuates that you're lusting after her, and personally sabotages all your attempts to bond with your classmates until the only people that talk to you are those that think you're into freaky sex and want in. And then she wonders why Nanase would think she wouldn't be normal about her buying a bra. After spending every second of every day insisting that she play this role and twisting every situation into some perversion. Of fucking course Nanase tries to get three seconds of peace, and when Karin re-enters the picture she immediately resumes horndogging on who she insists, in public, is her brother.
And thats not even touching the 20 year old and the 10 year old "in love". I try not to look directly at those.