Tsumitsuki

In the town that Takada Chinatsu moved to, there's a legend about demons called Tsumitsuki that possess the feelings of guilt a person has over their sins. Those who are possessed are slowly devoured, body and mind, as the demon manifests. As one of Takada's friends starts acting strangely, her classmate Kuroe steps in to help... but his true motives are hidden behind a mask.
(Source: Storm in Heaven)