Thunder, legally registered as Koichiro Sugiyama, is a high school judo athlete recognized for his raw power and athletic prowess, yet plagued by self-doubt during tournaments, where his meticulous training rarely translates to wins. His earnest commitment to the sport clashes with a tendency to falter under competitive stress, fueling persistent frustration.

Shion’s intervention marks a turning point: her rigorous coaching sharpens his techniques, though her effortless dominance in sparring sessions leaves him both humbled and captivated. This admiration blossoms into romantic feelings, culminating in a clumsily earnest confession during a mission to rescue her. Shion’s literal interpretation of social norms twists his awkward proposal into a comedic exchange, masking the sincerity beneath.

Hotheaded and decisive, Thunder champions aggressive strategies, such as leading a frontal assault on the Hoshima Corporation to reclaim Shion. His boldness underscores unwavering loyalty to his allies and a penchant for high-stakes gambles, cementing his role as the team’s emotionally charged motivator.

Beneath his fiery exterior lie insecurities about lagging behind peers, vulnerabilities tempered through shared trials and Shion’s unifying presence. As collaboration replaces solitary struggles, his initial hesitance morphs into steadfast teamwork, charting a journey from self-criticism to resilience forged in trust and collective purpose.