Riku experienced a lot of pain and tragedy in his early life. After his father's death, a former-boxer Yakuza man taught him how to do a basic punch, and that punch saved his life when he had to defend himself from his mom's drug dealer. He ended up taking the drug dealer's life, marking him as a killer. Criminals continued to come after him, leading to more tragedy for the people who attempted to care for him. All of this drove him to ask that same former boxer to teach him to become stronger, which led him to a rundown gym, his door to the world of pro boxing!

When he woke up, Souma Tetsujirou, a samurai from Kamakura who had survived the Mongolian invasion, found himself in an unfamiliar place.

He was told by Hrist, the girl who brought him there, that they were in Valhalla, a place where the souls of dead warriors congregate. In order for him to be revived, Tetsujirou now has no choice but to fight against the "dead warriors" from different eras in this mythical place of carnage that he's been thrown into.

This is the start of a samurai drama where one has to fight and strike down their enemies, even if it kills them!!