Story
Viper GTS is a hentai OVA of 3 episodes, produced by the Studio Moonrock and released in 2002. The three separate parts have been gathered into a movie when released in the USA.

In Hell. Carrera, Mercedes and Rati are three pretty succubi , who work for the devil Alphina. They are responsible for stealing human souls after satisfying their desires, and in that case, especially by having sex with them.

On Earth. Ogawa, a teenager, tired of being made fun by his peers, summons a devil, in order to solve this problem. But when he notices that he actually summoned the young, well-endowed Carrera, other ideas came to his head…

In episode 2: In Heaven, some angels detect an anormal number of missing souls on Earth. They quickly identify the succubi as the responsibles of this lack. In the same time, Carrera is imprisoned and punished because she didn't collect Ogawa's soul. Ogawa, bored, summons Mercedes instead; but when he can meet Carrera again, she is kidnapped by the angels…

In episode 3: Rati, summoned to rescue Carrera, is taken away by the angels too. Ogawa begs Alphina to come with him and Mercedes to save the two succubi. Then takes place then a final battle in Heaven, at the end of which Ogawa is seen with his three devil-friends having a lot of "fun".

Viper GTS is actually a tribute to the eponymous adult video game, produced by Sogna, well-known for its Viper series, that made bankrupt in 2000 and ceased its operations in 2003.