Hell Is Dark with No Flowers, Vol. 1 (manga)

Seiji Tohno sometimes sees the people around him as monsters. It's a curse that has driven him to a life of despair...but all that changes one evening when he stumbles across a bewitchingly beautiful boy in a huge European mansion. The boy introduces himself as Shiroshi Saijou, and before he knows it, Seiji has agreed to become Shiroshi's part-time assistant. It turns out that Shiroshi's "proxy service" is to consign yokai-possessed sinners to Hell, which will bring Seiji face-to-face with an unimaginable host of horrors!