Eight-Headed Giant Serpent's Counterattack (八岐之大蛇の逆襲, Yamata no Orochi no Gyakushū) is a 1985 fan film, the film's purpose was to serve as a sequel to The Birth of Japan. This film is one of GAINAX's most successful film. It was released on December 1985 and runs at 72 minutes.
Orochi in this film, has a more mechanical look, and is controlled by aliens that took over Earth many years ago. And come back to destroy Japan.