Waltz With A Black Cat summary:

Hirose is mad. Once again his boyfriend Matsui has cheated on him, with the sorry excuse of: "Sometimes I wanna see a girl's boobs more than a guy's d*ck." Crying at a nearby shrine Hirose curses Matsui... And the next day, outside Matsui's apartment, he finds a black cat with a scar just like Matsui! And Matsui seems to have DISAPPEARED... -Bakaupdates