|Game Debut||Danball Senki (PSP)|
|Anime Debut||Episode 01|
|Appears in||Game, Anime|
|Voice Actor||Yasuhiko Tokuyama|
|Occupation|| Former Black Division Agents|
Eclipse Head Pilot
|Affiliation(s)|| Innovator (defected)|
|LBX:||Deqoo, Deqoo Kai|
Masashi Hosoi (細井 将志) is one of Eiji Yagami's personal agents in the Danball Senki series.
He has light blue hair, a long face, and rather unique eyebrows for the series.
He is often seen as being silly, along with his comrades. However, he is loyal to whomever he works for. Deep down he has a love for piloting and LBX, prefering to enjoy life rather than scheming.
His first appearance was in episode 1, where he, Shouko Mano, and Heita Yabake aim to apprehend Rina Ishimori for stealing the Platinum Capsule. Under orders from Eiji Yagami, the three find the Platinum Capsule in the Misora Town neigborhood belonging to the Yamano family. Once inside, they discover Ban Yamano with the Platinum Capsule, so Masashi sends out his Deqoo alongside his team. At first they are able to threaten Ban, but when the boy activates AX-00, the three find themselves challenged as Ban fights back, ultimately destroying Heita's Deqoo. Angry, Masashi and Shouko send their Deqoos in one final charge, but much to his shock, is defeated when the superior LBX bifurcates his in half with Shouko's. Masashi requests to retreat back to the Innovator's HQ.
They return in episode 4, overseeing the match between Ban and a brainwashed Kazuya as part of their plan to steal the Platinum Capsule when Egypt destroys Achilles. They retreat after Achilles's new mode overwhelms Egypt with their mission in failure.
In a flashback explaining the events of episode 7, Masashi was involved with Professor Yamano's kidnapping as the pilot of the plane in disguise, steering them to the Innovator's hidden base. In the present, he and his fellow agents arrive at Kamiya Craft to discuss locating the professor to another location with Togorou Kamiya. As they all hear the alarm that Ban Yamano, Ami Kawamura, and Kazuya Aoshima have entered the base, Masashi offers to battle with his upgraded Deqoo Kai, but is rejected by Togorou.
- All three of the agents resemble the three villain stooges in Yatterman, in slight similarity with height, appearance and personality.
- He was originally an ace air force pilot before becoming an Innovater agent, demonstrated when he piloted Eclipse with no problems.