Dōma Jinnai began as a Sengoku-period samurai. His human life ended tragically when ninjas slaughtered his wife and child, igniting an all-consuming desire for vengeance against every ninja clan. Following his death, tentacled alien beings from the future resurrected him, rebuilding his body into an indestructible cybernetic entity with advanced technology. This transformation granted him functional immortality; he survives dismemberment, decapitation, and severe bodily damage, his wounds sealing with a sizzling "white fluid" and detached parts reattaching. His reconstructed form possesses superhuman strength, heightened durability that shatters conventional blades, and the ability to detach his head, which flies independently and fires laser beams. Despite his mechanical enhancements, he retains his original swordsmanship skills, wielding a katana with lethal proficiency. Jinnai serves as a key enforcer for the warlord Oda Nobunaga, who received futuristic weaponry and technology from the same alien forces. Jinnai's personal vendetta drives relentless killing sprees targeting ninja factions, especially the Iga and Koga clans. He employs brutal methods: ripping out throats, vertically or horizontally bisecting opponents, crushing skulls explosively, and dismembering victims in combat. His psychological state remains solely fixated on exterminating ninjas as retribution for his family's murder, showing no remorse or deviation. Nobunaga manipulates this singular focus, convincing Jinnai his immortal existence must be dedicated to vengeance even after the original perpetrators are eliminated. Throughout engagements, Jinnai demonstrates tactical adaptability, recognizing and countering ninja deception techniques like scarecrow decoys and drug-induced illusions. He pursues targets with relentless persistence, surviving multiple assassination attempts involving poison, explosives, fire, and coordinated team assaults. His narrative concludes when a dynamite-triggered rockslide causes his internal nuclear reactor to overload and explode, though opposing alien forces' involvement leaves his ultimate fate ambiguous. No significant evolution occurs in his motives or personality across appearances; he remains a consistent, implacable, vengeance-driven antagonist.