Kyoushoku Soukou Guyver II
English name: The Guyver: Bio-Booster Armor
Genres: Action, Adventure, Drama, Horror, Sci-Fi
Type: OVA, Episodes: 6
Aired: Oct 24, 1991 to Aug 21, 1992
Studio: Visual 80
Source: Manga
Rating: R+ - Mild Nudity
Synopsis:
Sho and his friend Tetsurou stumble upon an odd alien artifact while walking through the woods. Then, the alien artifact breaks free of its metallic bonds and enters Sho's body, turning him into the Guyver. With this new power, Sho must do battle with the evil Chronos corporation and their genetically enhanced Zoanoids, who seek to get the Guyver back into their labs. No one close to Sho is safe from Chronos. He must fight. 

(Source: ANN)