Kojiro Hyuga hails from a financially struggling family in Misato, Saitama, Japan. After his father's death in childhood, he balanced part-time jobs to support his mother and siblings alongside his football ambitions. He launched his football career at Meiwa Elementary School, initially playing as a defensive midfielder before shifting to striker, leveraging his powerful shot and aggressive approach. He later transferred to Toho Academy for middle and high school, wearing the iconic jersey #10. While at elementary school, Hyuga forged his signature "Tiger Shot," a high-powered, straight-range strike known for its aggressive trajectory. At Toho Academy, he built key partnerships with Takeshi Sawada and Ken Wakashimazu, creating combo techniques including the aerial "Toho Twin Shot" and the coordinated passing move "Toho Golden Duo." His Toho teams reached national tournaments but suffered significant losses before achieving a shared championship victory with Nankatsu in their third middle school year. Hyuga debuted internationally on Japan's U-15 team during middle school. As a forward for Japan Junior (jersey #9), he became the top scorer in the U-16 World Cup. However, deficiencies in post-play and tactical balance led to his temporary exclusion from the U-20 national team. This setback fueled intensive training, developing his aerial dueling, hold-up play, and the upgraded "Neo Tiger Shot" – a full-powered evolution of his original technique boasting SS-rank power and minimal drop-off. He later created the "Raiju Shoot" (Lightning Tiger) as a further advancement of his shooting repertoire. Following high school, Hyuga pursued a professional career in Italy. He initially signed with Juventus but saw limited playtime amidst strong competition. A loan transfer to Serie C club Reggiana followed, where he competed against Shingo Aoi's FC Albese for promotion. Throughout this period, he continued refining his skills, adding dribbling techniques like "Straight Line Dribble" and defensive moves such as "Raging Wave Tackle." Personality-wise, Hyuga exhibits fierce competitiveness, hot-headedness, and confrontational tendencies, particularly evident in early rivalries with Tsubasa Ozora. Off the field, he demonstrates loyalty to family and teammates, protective instincts toward close relationships, and resilience through adversity. His leadership manifests through captain skills like "One Shot, Certain Victory," boosting shot power during critical moments. He also displays tenacity when trailing in matches ("Fierce Tiger's Tenacity") and heightened performance under low-stamina conditions ("Tiger Heart"). Physically, Hyuga grew from 158 cm and 50 kg in elementary school to 180 cm and 70 kg as an adult. His technical development expanded to encompass dribbling, tackling, and combo techniques alongside his signature shots. Notable later innovations include the "Neo Drive Tiger Twin Shot," a collaborative super shot with Tsubasa Ozora requiring high synchronization and specific situational triggers.