The eminence in shadow, vol. 7 (manga) - daisuke aizawa

Cids shadowbrokering 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 this hard-boiled town, he decides to give his background character persona a break to try out a new role--a man of mystery who laughs in the face of danger! However, the legendary Red Moon that rises over Cids carefree head might be more than just an ill omen.