Based on the erotic game by Alice Soft.
Sid enters a tournament. Shortly after he is crowned champion, the fallen Angel Aquross infects him with a hideous disease that requires him to steal the life energy of Angels or be in constant pain. The only relief lies in a drug that kills the pain, but causes sexual urges that cannot be denied. Now, Sid must defeat the evil Aquross.
(Source: Anime News Network)
