At the Battle of Sekigahara in 1600, Toyohisa Shimazu is the rearguard for his retreating troops, and is critically wounded when he suddenly finds himself in a modern, gleaming white hallway. Faced with only a stoic man named Murasaki and hundreds of doors on both sides, Toyohisa is pulled into the nearest door and into a world completely unlike his own. The strange land is populated by all manner of fantastical creatures, as well as warriors from different eras of Toyohisa's world who were thought to be dead. Quickly befriending the infamous warlord Nobunaga Oda and the ancient archer Yoichi Suketaka Nasu, Toyohisa learns of the political unrest tearing through the continent. Furthermore, they have been summoned as Drifters to fight against the Ends, people who are responsible for the creation of the Orte Empire and are trying to annihilate the Drifters. As the Ends grow more powerful, so does the Empire's persecution of elves and other demihumans. It is up to Toyohisa and his group of unconventional heroes to battle in a brand-new world war to help the Empire's subjects, while challenging the Ends protecting the land to claim it for themselves.

Touma Kusaka stands out from the rest of the Choshu Clan, as he does not share their anti-foreigner sentiment. After reuniting with Keiichirou Akizuki, a vassal of the Tokugawa family who once helped him escape from government authorities, the pair begin studying English in secret. As they continue to meet behind their feuding families' backs, romance between the two begins to bloom. But with war looming on the horizon between their respective clans, Kusaka and Akizuki's hope for a world where they can be together may never come to fruition if their obligations and bloodlines get in the way.

The story takes place in Japan. The year is 2030 and Earth has been completely overrun by a viral disease named Gibia that turns infected people into various different monsters, based on their age, sex, and race. A samurai and a ninja from the early Edo period travel together through time and arrive in a ruined Japan to aid a professor working on a cure for the virus. Together, they fight countless Gibia monsters, outlaws, and other fierce foes on their journey to save mankind.

The Sengoku era gave birth to many historical legends. One of them is Naoe Kanetsugu, the brilliant military general of the Uesugi family. Together with Maeda Keiji, a legendary warrior on the battlefield, who become lifelong friends with each other, they carve out a piece of history in the most dangerous and volatile time in Japan's history. The two men recall their beginnings and the journey they took to get to the accomplished position they now sit at.