Imouto no Oshi ga Warui Otoko da Nante Yurusanai

Koichi Fujikawa's younger sister is absolutely obsessed with Ryu, the center of the popular idol group CRown Sugar. One day, his class is abuzz with rumors of a new transfer student—who turned out to be Tatsuki Amada, AKA Ryu, his sister's favorite idol! While Koichi is excited to meet Ryu in the flesh, it seems like the guy is a bit...dangerous? (Source: Eiwa Publishing, translated) *Note: Includes one extra chapter.*