The end of the Bakumatsu era saw the decline of the samurai and the rise of yakuza. Shinjiro Oto dedicated his youth to mastery of the sword, and became the ideal samurai. His battles left him half-blind, but by the age of 25 he was granted the option to retire from the sword, having raised the next generation of samurai to combat the yakuza explosion. With the promise of a luxurious life waiting for him, he eagerly enters the hall where his retirement party would signal the abandonment of the samurai way.

Samira Nana, a graduate student living in modern Japan, drops everything and travels alone to Shinjuku a month after the death of her father, the head of the Nanagumi yakuza which rules Tokyo. With the goal of following in her father's footsepts and bringing the samurai way back to the yakuza, Samira becomes the target of remaining gang leaders as she seeks out a man said to be able to summon just the protection she needs: a samurai from the past.