Colt M1851 Zangetsu

In his pocket, a black iron pistol. In his heart, a jet black soul.

The story takes place in Edo in 1853. Nicknamed Zangetsu, Rouji is a young head clerk at the Mitakaya wholesale shipping agency. He has a bright future ahead of him, but behind his affable mask hides an important member of the Yoshihira faction, rice brokers who control the Edo underworld. He plans to rise through the ranks of the organization, and his weapon of choice is the Colt M1851 Navy, the most advanced revolver of the time! With his skill in handling weapons and his innate courage, Rouji tries to work his way up in the Edo underworld...

(Source: Kadokawa, translated)