DoS Obake ga Nekasetekurenai

When salaryman Yuji's straight crush invites him to his marriage, he decides that now is the time to get super drunk. He knows he falls asleep all alone in his apartment, but why does he vaguely remember someone's hands and mouth on him...and wake up to a very special taste on his tongue? If this is really a ghost, why is this haunting very R18? (Source: Manga Planet) Note: Includes three extra chapters.