Topjoy is a basketball Leaguer with an extremely perky and optimistic personality, reinforced by cheerful music constantly playing from his shoulder speakers. He displays a strong affinity for children, often playing with Hiroshi and other kids. Initially approaching sports purely for enjoyment like Mach Windy, his showboating and ball-hogging tendencies caused his expulsion from his original team. Despite regularly proclaiming himself the greatest basketball Leaguer, he frequently committed significant gameplay errors. After dismissal, the Dark Intelligence Service Section X recruited him to infiltrate Silver Castle as a spy.

Topjoy's integration into Silver Castle was complicated by his conflicting sportsmanship mindset, yet his cheerful disposition helped him quickly assimilate as a mood maker. He bonded with the team's five child supporters, while Silver Castle members intervened to curb his rough play. His childish personality and reluctance to harm teammates undermined his effectiveness as a spy. A shock circuit installed by Dark inflicted punishing pain, and combined with his desire to return to professional basketball, this prevented him from severing ties with the organization, causing intense suffering. His internal struggle persisted until Magnum Ace's exposure led to Topjoy's isolation within Dark. Silver Castle friendships proved pivotal during this period, helping him overcome the crisis. Magnum Ace eventually removed the shock circuit, freeing Topjoy from Dark's control.

Physically, Topjoy has spring-based arms and legs granting exceptional jumping ability and expansive throwing range. His signature technique is the "Galactica Pegasus Shoot," and he developed collaborative moves like the "Mistral Bomber" soccer technique with Mach Windy. Beyond his personal journey, Topjoy positively influenced other Leaguers, notably rehabilitating Guevara—a feral basketball Leaguer living in the jungle—which solidified his place in the team dynamic.