Tasuku Ryūenji is a middle school student and a prominent member of the Buddy Police, an agency that handles crimes involving monsters and card battles. He initially uses a Dragon World deck, and his Buddy monster is Jackknife Dragon, a green dragon with whom he shares a deep, familial bond. Their buddy skill, Sky Circle, enables flight, and his core gadget is the Star Pulser. His past is marked by tragedy, as he was present during "The Disaster," where he first encountered Jackknife Dragon before being rescued by the Buddy Police, an event that led him to join their ranks. This experience fostered his belief that adults over-shelter children, fueling his drive to prove his independence and maturity. His sense of justice was once corrupted by Kyoya Gaen, leading him to temporarily join the organization Disaster under the alias "Purgatory Knight." During this time, he used a Darkness Dragon World deck with Demios Sword Dragon as his Buddy and employed a Dark Core gadget for armor. His personality grew colder and more hostile, adopting Kyoya's view that adults are the root of the world's problems and that children are powerless. He also struggled with self-hatred for being unable to help his family during The Disaster. He eventually returned to his senses and reunited with Jackknife Dragon. He later adopted a Star Dragon World deck, and his Buddy evolved into Star Guardian Jackknife and then Star Dragoner Jackknife after repairs. Equipped with interstellar weapons, he continued his duties, occasionally stepping back from the Buddy Police to focus on his studies but remaining active in buddyfighting. Tasuku possesses a cool yet kind personality, which makes him popular. He is generally mature for his age and often sees himself as an adult, preferring not to associate with children. However, he can be an airhead, such as when he mistakenly called Noboru Kodo "Kitten Shirt" or failed to realize he couldn't enter an abandoned shaft without a buddy skill. His strong sense of justice drives him to take risks or defy orders to protect others, a trait Kyoya Gaen exploited. He is also very forgiving, offering redemption to others like Rouga Aragami. This powerful sense of justice has sometimes led to stubbornness and extremes, influenced by his trauma from The Disaster. After his time as the Purgatory Knight, he felt disheartened, shocked, and ashamed, initially believing himself unworthy of being Jack's Buddy. With Jack's encouragement, he overcame these feelings, though guilt lingered in subsequent seasons. In later developments, he becomes a high-ranking officer in the Buddy Police, known as the Commissioner. He maintains a friendly rivalry with Gao Mikado, and they often collaborate. He temporarily steps down from Buddy Police duties to focus on studies but continues participating in adventures, helps other buddyfighters train for tournaments like the World Buddyfight Championship, and uncovers hidden abilities in Gao's new buddy, Bal Dragon. He gains special abilities such as Future Force, activated through his core gadget, and Dragon Force forms like the Dragon Force of Joy and its evolution, Dragon Force "Style of Justice," which involve power glows, crystals, and a fairy-like appearance. His appearance evolves across seasons. Initially, he sports white/blue hair spiked on the left side and pinkish-red eyes, wearing an orange Buddy Police vest with a symbol, pauldrons, a teal jumpsuit, a black shirt, orange fingerless gloves, and elbow pads. His school uniform consists of a blue coat with dark blue and red accents, a blue tie with red lines, a white button-up shirt, blue pants, and brown shoes. In Season 2, while fighting for Star Dragon World, he dons white and yellow space armor with green highlights and an orange space belt. In Seasons 3-5, he wears a white and blue shirt with two black lines, a light blue space in the middle, blue and grey shoulder pads, black sleeves, blue pants, and black boots.