Jin Tadokoro, nicknamed "Old man, The Bear," stands as a prominent cyclist and former third-year vice-captain of Sohoku High School's bicycle racing club, where he reigned as ace sprinter. His early cycling career was marred by struggles with his large physique, causing poor performance on climbs. First-year failures included last-place finishes in the Minegayama Race and First-Year Welcome Race, plus dropping out on a training camp’s second day. Frustrated by ineffective weight loss and diet-induced weakness, he nearly quit until then-captain Toji Kanzaki intervened. Kanzaki redirected Tadokoro toward his innate sprinting talent, training him with Coach Pierre while instilling the belief that limits are self-imposed. This mentorship forged him from a disheartened novice into a powerhouse sprinter, earning his Inter High team spot by second year. Physically imposing with straight black hair, sharp brown eyes, and towering height—tying as tallest in Sohoku’s initial lineup—Tadokoro’s angled eyebrows often mask his complexity. Loud and competitive, he boasts about victories and clashes with spirited teammates like Shoukichi Naruko. Yet he reveals vulnerability, flustering easily when coaxed into singing anime themes or facing Akihabara’s cosplay maids. He carries fierce responsibility toward juniors like Junta Teshima and Hajime Aoyagi, mentoring them with tearful reactions to their hardships and physical affection like back-clapping. He hides perceived weaknesses, dismissing illness as a mere "handicap" for rivals during the Inter High. His racing style exploits extraordinary physiology: an 8,500cc lung capacity—nearly double average—fuels the "Mach Speed Oxygen Human Bullet" technique. Deep inhalations flood muscles with oxygen, curbing lactic acid for explosive sprints. His bulk shields teammates from wind, even uphill, earning monikers like "Human Bullet Train." Victories include the Bay Coast Criterion photo finish against Naruko and Aoyagi, plus wins in the Last Autumn Race and Bay Coast Criterium. Beyond high school, Tadokoro races for Tukushiba University yet remains loyal to Sohoku, frequently supporting former teammates. Key bonds include his rivalry-turned-respect with Naruko, protective ties to Aoyagi and Teshima, and foundational camaraderie with third-year peers Kinjou Shingo and Yusuke Makishima. A pivotal clash saw him punch Hakone’s Juichi Fukutomi after Kinjou’s crash injury, though reconciliation followed upon recognizing Fukutomi’s remorse. Personal facets include his family’s bakery, kendama and Sengoku-era gaming hobbies, speed-eating talents like a 7.5-minute ramen record, and quirks such as preferring VHS tapes and recycling bottles via his "Rampaging Human Bullet Vacuum" method.