The Eminence in Shadow, Vol. 7 (manga) by Daisuke Aizawa

Cid’s shadow brokering fun is interrupted when his sister, Claire, drags him off to the Lawless City to hunt some vampire called the“Blood Queen” or something. To fit in with the atmosphere of this hard-boiled town, he decides to give his normal background character person a a break and try out a new role—a young man who laughs mysteriously at the violence around him! However, the legendary Red Moon that rises over Cid’s care free head might be more than just an ill omen…