Mitsuru Hanagata, son of the Hanagata Motors owner, spent early childhood in Yokohama before five years in England during kindergarten. Facing discrimination as a "yellow Jap" there ignited a fierce drive to excel in soccer, horseback riding, fencing, and tennis, culminating in an audience with Queen Elizabeth II. Returning to Japan brought disillusionment with his homeland and family, leading to delinquency. By elementary school, he drove sports cars illegally and formed the Black Shadows baseball team, developing his "Knockout Batting" technique. Witnessing Hyūma Hoshi's pitching and secret training gear prompted a recruitment attempt. After Hyūma defeated him and broke the Knockout Batting, Hanagata acknowledged him as his eternal rival.

At Kōyō High School in Kanagawa, Hanagata worked to make the baseball team contenders for the Kōshien Tournament. He intervened in Hyūma's educational struggles by offering tuition money through Hyūma's sister Akiko, angering Hyūma and causing tension. Their rivalry intensified during a Kōyō red-and-white match where Hanagata, despite an injured hand, confronted Hyūma over perceived pity pitching, leading to a fight and eventual reconciliation. Hanagata later orchestrated a broadcasted game against Hyūma's Seiun High School to force Hyūma onto the mound, though their direct confrontation remained unresolved. At the Kōshien finals, Hanagata hit a game-winning home run off an injured Hyūma, unaware of the thumb injury's severity. Learning the truth from the bloodstained ball, he embraced Hyūma on the mound. This act inadvertently contributed to the dissolution of Seiun's team and Hyūma's expulsion.

After high school, Hanagata sent the bloodstained ball to the Yomiuri Giants to highlight Hyūma's determination, an act which backfired by increasing the Giants' manager's displeasure with Hyūma. Initially selected for the All-Japan team bound for Hawaii, Hanagata switched to the Hanshin Tigers upon learning of Hyūma's Giants enrollment. He inherited the Tigers' permanent number "10" jersey, previously worn by legendary hitter Fujimura Fumio. As a professional, Hanagata initially succeeded against Hyūma's pitches but later fell into a severe slump after being bested by Hyūma's "Dai League Ball No. 1." Determined to overcome this, he underwent extreme special training, hitting iron balls with an iron bat at a Hanagata Motors subcontractor factory. This training enabled him to hit a home run off the improved pitch, but resulted in serious injuries including broken bones and muscle damage. His fixation on countering the Dai League Ball led to an inability to hit normal pitches, causing his temporary removal from the Tigers' starting lineup. During a critical Giants vs. Tigers game, Hanagata pleaded with his coach for the chance to face Hyūma directly.

Expanded narratives like the 2002 anime "Special Edition: Fierce Tiger Mitsuru Hanagata" and the manga "Shinyaku 'Kyojin no Hoshi' Hanagata" delve deeper into his UK childhood, leadership of the Black Shadows, and complex relationships, including with Akiko Hoshi, reframing the original story from his perspective and emphasizing his unwavering sense of justice, loyalty to friends, and pride. His character displays a chivalrous yet overconfident demeanor, marked by his dismissive catchphrase, "I don't have a name to give to you," reflecting his aristocratic upbringing and competitive resolve. His arc consistently depicts his evolution from a disillusioned delinquent to a professional athlete intrinsically tied to his rivalry with Hyūma Hoshi.