Based on the information available, a comprehensive character description of Hiroshi from the anime Thunder 3 cannot be provided. The search results offer only very limited details about this character.

Hiroshi is known to be one of the three main protagonists in the story, forming a trio with his friends Pyontaro and Tsubame. The three are ordinary middle school students who are collectively nicknamed the Small Three. Along with his friends, Hiroshi discovers a parallel world after playing a mysterious disc, leading to an adventure when Pyontaro's younger sister, Futaba, is pulled into this other dimension and captured. In the hyper-realistic parallel world, Hiroshi and his friends discover that their cartoonish, chibi-like bodies grant them superhuman strength and resilience. This forms the core of the group's role in the story, as they journey to rescue Futaba. Hiroshi's voice actor has been announced for the upcoming anime adaptation.

No information is available in the provided search results regarding Hiroshi's specific personality, his individual motivations beyond the group goal, his personal background, his key relationships beyond being part of the central trio, any character development he may undergo, or a detailed list of his notable abilities separate from the general power shared by the group. For these missing details, no info.