From MangaHelpers:

With the end of the feudal era in Japan and peace finally spreading throughout the land, the warriors and the samurai who were once vital to the war have lost their place in society. But just because they are no longer needed doesn’t mean their blood thirst has been quenched. These lost souls still kill people out of nature and innocent people are being harmed. Jirai has been tasked with finding and eliminating these people as a “killer of killers.” With his demonic right hand that serves as a weapon stronger than anything man has ever made, he brings peace to fallen warriors. [vyc]