Yamu Zokusei Giri Giri Onee-ChanYami Zokusei Giri Giri Onee-chan; 病み属性義理ギリ姉ちゃん; Sick Attribute Step Sister

A young man meets his new step-sister, an asocial shut-in with messy black hair and massive breasts who is obsessed with him. Do I really need to elaborate?