Shimazu Toyohisa is the real-life samurai who fought in the pivotal Battle of Sekigahara. In his dying moments, Shimazu is transported to a world of magic with other famous warriors throughout history. These warriors are forced to fight each other in an endless battle.
A gate appears in Tokyo's Ginza district sometime in the 21st century. From the gate pours out monsters, knights from middle-age Europe, and other fantasy-like beings, and they kill many of the citizens of Tokyo. This event is known as the Ginza Incident. The government sends a small group of soldiers from the Japanese Self-Defense Forces to the alternate world beyond the gate. Led by otaku soldier Yōji, they find that the villages in the world are being attacked by a dragon. An elf girl who is a survivor from the dragon's rampage joins the group in their travels across the dangerous new world.
During the Hundred Year's War between England and France in the Middle Ages, a powerful witch named Maria lives in a secret forest with her familiars. She hates the war around her, and will sometimes stir up trouble against the church that does nothing to stop it. Her interventions into the world, however, run against the plans of heaven, earning her the attention of the Archangel Michael.
Kenshi Masaki is the half brother of Tenchi Masaki and used to live in Japan, that is until he was summoned to the land of Geminar. The Land of Geminar has been witness to an endless amount of wars that have been fought using Seikijin, bio-mechanical weapons controlled by a capable warrior called a Seikishi using magic power called Ahou. It is revealed that Kenshi is an amazing Seikishi and it seems someone has a reason for Kenshi to be in Geminar, but who and why are not known.