There was once an ogre (oni) mother who gave birth to a human looking child. Instead of an ogre's horn, this child was born with a sword in hand called the "Onikirimaru" or Ogre Slayer. He has no name and is only referred to by the name of his sword. Though he appears human, he is pure ogre. Believing that he will become human once all of his kind have vanished from the world of humans, he sets out on his destiny to slay all of his kind. Even now, in the mother world of Japan, he is still out there slaying ogres.

In the future, mankind can no longer live on the ground due to intense radiation, both from the sun and from an abandoned nuclear plant. One day, a group of special police raided a religious cult compound, and after a fierce firefight two policemen found a winged mutant girl, with chains on her arms, barely alive. However, government scientists dressed in hazardous material suits immediately intervened and brought her back to a research facility. Realizing they were merely transferring her from one prison to another, those two policemen formulated a daring plan to set her free once and for all.

After battle in first season battleship Amanohara was serious damaged and need to repair. It land on island where a Gogyou festival just begin. Umakai Shintaro and his five girls student who know as Raimu Unit begin enjoy a peace time in that island. But the enemy still follow them around. How Umakai Shintaro and his five girls student fight against the enemy. Still his five girls student begin try to draw his attention into them.

Orihara Kouhei returns to his town after a long disappearance to fullfil the promises he made to several girls in his childhood. He suffered from memory loss, and carries a tragic past. An strange ambience surrounds the OVA...It's almost like a dream, like memories from the past trying to come together in one piece but without being able to...