Kyomu Senshi Miroku
Japanese title: 虚無戦史ＭＩＲＯＫＵ
Alternative titles: Expunged Chronicle of Miroku
Type: OVA
Source: Manga
Episodes: 6
Status: Finished Airing
Aired: Jan 10, 1989 to Nov 5, 1989
Duration: 25 min per ep
Rating: R+ - Mild Nudity
Producers: J.C.Staff, animate Film
Genres: Action, Fantasy, Sci-Fi, Supernatural
Themes: Historical, Mythology, Samurai

A psychic ninja fantasy suggesting that the assassins did not die out during the Sengoku era but burrowed under Japan, where they fought a new war against the alien occupants of a crashed spaceship that has lain undisturbed for several millennia. 

(Source: The Anime Encyclopedia)