The story of a man and a woman that extends over 30 years in the Warring State period.

Before he was a protector, Kenshin was a fearsome assassin known as Battosai. But when he meets the gentle Tomoe Yukishiro, his story begins to change.

Alien pods come to Earth and, naturally, start taking over Human Hosts. One such pod only manages to take over one human's, Shin Izumi, right arm. Together they grow and co-exist, all the while the other aliens are making meals of other humans; Shin feels he must put a stop to it all, but his alien, Migi, doesn't see why.