Suteneko Sagashimasu.

Keigo Odagiri runs a detective agency in an old, run-down building on the outskirts of Tokyo with his assistant, Leo. All they get are relatively trivial cases, but they're happy as long as they have each other. They spend their days eating, sleeping, and after doing a little work, making love. Their simple, everyday life together is sweeter than anything... This is a romantic story about two kind and gentle men!!

(Source: Renta!)