Toumei na Ai no Utsuwa

Miki Donoue has lived a life of full misfortune since childhood. Kind but timid, he has always kept alone to himself to prevent others from being caught up with his misfortunes. One night, he is approached by a mysterious man who asks him, "Can you give me your misfortune?" The man claims to be a "akashibito," a monster that feeds on human misfortune to sustain its life, and he claims that he malnourished and near death.
The good-natured Miki names the monster "Shiro" and decides to take him in to feed him energy. Shiro's pure devotion to his human host is a source of joy, and he soon finds himself attracted to Miki. But as his days are filled with happiness, something begins to happen to Shiro's body...?
(Source: onBLUE, translated)
Note: Includes one bonus chapter.