Mitsuru Hanagata grew up in the United Kingdom, where childhood discrimination fueled his fierce competitiveness. He mastered soccer, horseback riding, fencing, and tennis, earning recognition including an audience with Queen Elizabeth II. Returning to Japan, disillusionment with family and society led him into delinquency: driving sports cars illegally and founding the delinquent baseball team Black Shadows. His rivalry with Hyūma Hoshi ignited when Hyūma shattered Hanagata's "Knockout Batting" technique, cementing their lifelong competition. At Kōyō High, Hanagata revitalized the baseball team, steering them toward the Kōshien tournament. He secretly funded Hyūma's tuition through Hyūma's sister Akiko Hoshi to prolong their rivalry—a revelation that later sparked conflict between them. Hanagata played through a leg injury sustained aiding a friend, showcasing his loyalty. During Kōshien, he hit a decisive home run off an injured Hyūma, unaware of his rival's condition. After learning the truth, Hanagata embraced Hyūma on the mound, inadvertently causing Hyūma's team disbandment and expulsion.

Upon Hyūma joining the Yomiuri Giants, Hanagata immediately enlisted with rivals Hanshin Tigers, inheriting jersey number 10. As a pro, initial struggles against Hyūma's pitching drove him to extreme training: wielding an iron bat against steel balls. This regimen caused severe injuries like fractures but underscored his relentless pursuit of victory. The spin-off *Special Edition: Fierce Tiger Mitsuru Hanagata* expanded his backstory, detailing his UK childhood, delinquent phase, pro challenges, complex bond with Akiko Hoshi, and psychological rivalry with Hyūma.