Variable Pipers II – Infinite Pleasure [English], an hentai doujinshi parodying the Viper series, by Graf Zeppelin
A long time ago, the Viper animated hentai gifs were pure gold. There’s not much left from that era, I don’t regret it much ^^
Here, as a brief blast from the past, here is a decent parody, in which one of the female chars has sex. Crude and hardcore, not much more to add, frankly, save for a warning: brace yourselves, folks, for the last page, the credit page, is something entirely different
Release credits are for Red Piotrus, Ultimaflaral and Ongokakashi, from the E-H Cove, thank you ^^