Mitsuru Hanagata, born into wealth as the son of Hanagata Motors' owner, spent five childhood years in the United Kingdom for education. There, discrimination as a "yellow Jap" fueled his competitive drive to excel in sports and academics. This effort earned him an audience with Queen Elizabeth II, but achieving it left him purposeless. Returning to Japan, disillusionment with his family and society led him into delinquency. By elementary school, he drove sports cars illegally and formed the delinquent baseball team, the Black Shadows.

His first encounter with Hyūma Hoshi happened when Hyūma broke Hanagata's signature "Knockout Batting" technique. Witnessing Hyūma's pitching ability and dedication fostered Hanagata's deep respect, beginning their lifelong rivalry. After this defeat, Hanagata entered Kōyō High School in Kanagawa Prefecture and transformed its underperforming baseball team into a Kōshien Tournament contender.

During high school, learning of the Hoshi family's financial struggles, Hanagata offered tuition money to Hyūma through his sister, Akiko. This angered Hyūma, leading to a physical confrontation where both exchanged punches, ultimately strengthening their mutual respect. Their rivalry intensified in a game between Kōyō and Hyūma's Seiun High School, where Hanagata manipulated circumstances to force Hyūma to pitch. The game ended inconclusively due to strategy and interference, solidifying their competitive dynamic.

In the Kōshien Tournament finals, Hanagata hit a game-winning home run off an injured Hyūma, initially unaware of the thumb injury affecting Hyūma's pitch. Discovering blood on the ball and realizing Hyūma's condition, Hanagata embraced him passionately on the mound. This act inadvertently contributed to the disbanding of Seiun High's baseball team due to the fury of key benefactor Daizō Ban.

Upon learning of Hyūma's recruitment by the Yomiuri Giants, Hanagata immediately joined their arch-rivals, the Hanshin Tigers, adopting the permanent number "10" as a symbol of his stature. Professionally, Hanagata initially succeeded against Hyūma's fastballs but struggled against the newly developed "Dai League Ball No. 1." 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 pitch, though the impact caused severe upper-body injuries, including broken bones and muscle damage.

Hanagata's perspective and development received expanded focus in the spin-off series "Special Edition: Fierce Tiger Mitsuru Hanagata," which recontextualized events from his viewpoint. It highlighted his childhood adversity in the UK, his complex relationship with Akiko Hoshi, and his internal struggles. The series reinforced the depth of his rivalry with Hyūma, depicting their confrontations as central to both characters' growth across high school and professional leagues, and included new scenes exploring his emotional conflicts and personal sacrifices.

Throughout his career, Hanagata maintained a complex but respectful relationship with Hyūma, often intervening on his behalf during personal crises, like protecting him from ambushes by former Black Shadows members. His character evolved from a privileged delinquent to a dedicated athlete whose relentless drive was inextricably tied to his rivalry with Hyūma, shaping his identity across all official media iterations.