Tasuku Ryuenji serves as the series deuteragonist, a seventh-grade student initially working for the Buddy Police before taking leave for studies. His past is marked by "The Disaster," where he was stranded in the mountains and rescued alongside his future buddy monster, Jackknife Dragon. This trauma fuels his belief that adults over-shelter children, driving his premature quest to prove independence and maturity. Physically, Tasuku possesses distinctive white-blue hair spiked leftward and pinkish-red eyes. His attire evolves across seasons: Seasons 1-2 feature an orange vest with the Buddy Police symbol over a teal jumpsuit and black shirt, plus orange fingerless gloves and elbow pads; his school uniform is a blue coat with dark blue/red accents, blue tie, white button-up, blue pants, and brown shoes. Season 2 adds white and yellow space armor with green highlights. Seasons 3-5 shift to a white and blue shirt with black lines, blue-gray shoulder pads, black sleeves, blue pants, and black boots. Personality-wise, Tasuku exhibits a cool, mature demeanor coupled with deep-seated kindness that garners admiration. He often avoids peers, preferring adult company. Despite his maturity, he occasionally acts airheaded, misnaming people or overlooking practical constraints. His intense but flawed sense of justice leads him to risk safety and disobey orders to protect others—a trait exploited by Kyoya Gaen. This manipulation corrupts his ideals, prompting him to join the villain group Disaster as "Purgatory Knight." In this role, he adopts a cold, hostile worldview, blaming adults for global problems and viewing children as powerless. He harbors crushing guilt over failing to save his family during The Disaster. His bond with Jackknife Dragon is profound; they treat each other as family and willingly sacrifice for one another. After his time as Purgatory Knight, overwhelming guilt and shame leave him feeling unworthy of Jack until encouragement aids his recovery. Season 2 shows him grappling with lingering guilt and briefly emulating rival Gao before overcoming these feelings. His story begins in Season 1 as a Buddy Police officer wielding a Dragon World deck, with Jackknife Dragon as his buddy and the "Star Pulser" core gadget. He first appears apprehending a fugitive using his signature card, Gargantua Punisher. After losing a friendly match to Gao, he declares him a rival and gifts him Gargantua Punisher. He later confronts antagonist Wolf using the restricted ability "Future Force" for combat advantages. Suspended for unauthorized Future Force use, he grows disillusioned with Buddy Police bureaucracy. This culminates in his defection to Disaster as Purgatory Knight, wielding a Darkness Dragon World deck, armored Dark Core gadget, and Demios Sword Dragon as his buddy. His fall includes impassioned rants about adult corruption and child powerlessness. Unmasked and defeated, he expresses profound regret and temporarily steps away from buddyfighting. In *Future Card Buddyfight Hundred*, he trains in Dragon World and returns with a Star Dragon World deck and upgraded buddy, Star Guardian Jackknife. Desperation to rescue Jack from a dystopian future triggers his luminous "Dragon Force of Joy" super mode. Key events involve traveling to a Hundred Demons-overrun future, reuniting with a blinded Jack, and learning this future stems from failing to stop the demon Yamigedo. He also works undercover in a buddyfight club and partners closely with characters like Gaito. By *Future Card Buddyfight Ace*, he ascends to commissioner of the Buddy Police. His arc spans traumatic loss, moral corruption, redemption, and eventual leadership, consistently anchored by loyalty to Jack and commitment to justice.