Nemurenu Hitsuji to Kodoku na Ookami is a series from Clockup with 2 titles.
Takeo is an ordinare janitor, living in a love hotel. Because he is suffering from chronic insomia, he can't go to sleep well, except if he kills someone. Thus he works secretly for a gang as an assasin in order to sleep peacefully. Although the many dangers in his life, his everyday life was relativly stable and peaceful.
This all changed when he met a girl called Azami. With her, he had the best sleep ever, so he thought about heeping her. But, the boss he is working for is chasing this girl, thus destroying his peaceful life