Tenkai, a high-ranking Bakufu agent, cloaks his true role as commander of the oniwabanshū secret police beneath the guise of a Buddhist monk during the Bakumatsu era. Driven to secure Captain Kidd’s legendary treasure and prolong the Tokugawa Shogunate’s isolationist reign, he meticulously orchestrates bloodshed and betrayal. His machinations include slaughtering Jirō’s adoptive family to frame the youth, forcing him into exile while positioning himself as Jirō’s savior and mentor. This calculated mentorship masks Tenkai’s exploitation of Jirō’s lineage—years earlier, he tasked Jirō’s father, Tarōza, with locating the treasure, only to order Tarōza’s assassination when he abandoned the mission for love. Tenkai later manipulates Jirō into unknowingly killing his own father, disguising the patricide as retribution for the adoptive family’s murder.

A shadowmaster of deception, Tenkai employs body doubles to evade death and sustain his grip on power. His influence stretches beyond Japan’s borders, entangling foreign agents and historical figures like Mark Twain and Geronimo in Jirō’s global hunt. Aligning with pro-Shogunate forces during the Boshin War, he fuels political turmoil to crush imperial dissent. Tenkai’s cruelty extends to psychological warfare: he molds loyalists like Oyuki—later revealed as Jirō’s half-sister—into devoted tools and stokes historical rivalries to erode adversaries.

His imposing frame and monk’s staff, concealing a lethal blade, mirror his dual nature of piety and violence. The collapse of his schemes unfolds during Hakodate’s fall, where he confronts Jirō in a final duel. Though earlier decoys feigned his demise, the true Tenkai emerges, only to meet his end impaled on the Dagger of Kamui. His death coincides with the Shogunate’s downfall, extinguishing an era shaped by his venomous ambition.