Masashi Hosoi is a supporting character in the Danball Senki series, also known as LBX: Little Battlers Experience. He is one of the personal agents working under Eiji Yagami, serving as an operative for Yagami's organization. Originally a highly skilled ace pilot, Hosoi retains his exceptional piloting abilities throughout the series, demonstrating considerable expertise in LBX combat. He appears in both the original Danball Senki series and its sequel, Danball Senki W.

In terms of appearance, Hosoi has light blue hair and a long face with distinctive, uniquely shaped eyebrows that make him stand out among the cast. His demeanor is often characterized by a silly or goofy nature, particularly when interacting with his fellow agents. Despite this lighthearted side, he remains fiercely loyal to the organization he serves and to the individuals he works for. He is typically seen alongside his comrades, and their interactions often carry a comedic tone.

Hosoi is known for his use of the LBX model Deqoo, which serves as his primary machine in battle. His background as an accomplished pilot means he is more than capable in combat situations, and his skills remain sharp even as the story progresses. Within the narrative, he fulfills the role of an antagonist agent, opposing the main characters as part of Yagami's plans. However, his personality and interactions prevent him from being a purely menacing figure, instead presenting him as a competent yet occasionally humorous operative.

Throughout the series, Hosoi does not undergo major personal transformation, but he consistently carries out his duties as an agent, contributing to the conflicts and challenges faced by the protagonists. His key relationships are with Eiji Yagami, his superior, and with his fellow agents, with whom he shares a sense of camaraderie and mutual reliance.