From 2D Market:
Meet Chisato Mashiro, a seemingly typical young girl who only thinks of boys and dates with her senpai.
Normally a quiet, docile girl, she’s nevertheless going through her rebellious period and the target of her outbursts is typically her uncle. He’s distraught that the sweet little girl that always played with him has grown to be so foul-mouthed (though he doesn’t mind some other parts of her that have grown too.)
One day, Chisato catches her uncle rummaging through her underwear drawer while she was not supposed to be around. Enraged, she lets out a torrent of verbal abuse and threats.
Hearing that, the uncle finally snaps. Realizing that he’s beyond the point of no return, he decides to take matter into his own hands and take a more active role in his Chii-chan’s upbringing...