Masamitsu Seki is a supporting character in the anime Bokurano. He is an officer in the Japanese Air Self-Defense Force, holding the rank of Lieutenant Senior Grade, and serves as the air force representative within Morimoto’s staff, working closely with his colleague Tanaka. His decision to join the military was originally inspired by his fascination with the fictional mecha anime Idol Defense Force Hummingbird.

Seki is portrayed as a straightforward and disciplined soldier with a cold, calculating demeanor. He is often regarded as the brains of the group, possessing sharp tactical and strategic thinking that makes him a valuable asset in planning how to confront enemy robots. Despite his outward reserve, he genuinely cares for the well-being of the children who have been forced to pilot Zearth, and he takes steps to support and protect them when possible.

After several of the original child pilots die in battle, Seki becomes one of the adult volunteers who signs a contract with Koemushi to fill the empty seats in Zearth’s cockpit. Prior to signing, he threatened Koemushi with a gun, which led to Koemushi teleporting away Seki’s right arm, leaving only the hand that held the weapon behind. By the time Seki and Tanaka formally enter the contract, his lost arm has been replaced with a mechanical prosthetic. Unbeknownst to him, this prosthetic contains sensors secretly planted by Kanji Yoshikawa’s mother, intended to gather intelligence on Zearth’s technology and the true nature of the battles.

During Kanji’s battle, Seki makes a sacrifice that allows Kanji to defeat the enemy robot, thereby creating another open seat. However, in the anime adaptation, Seki survives this encounter. In fact, he becomes the only contracted pilot to live through the entire series.

Seki’s role in the story is that of an adult authority figure who gradually becomes embroiled in the children’s tragic situation. His character develops from a mere military officer with a superficial anime-inspired motivation into a key participant who bears physical loss and ultimately outlives the other pilots. His notable abilities include his tactical acumen, his competence as a soldier, and his use of the prosthetic arm, which later serves as an unintended surveillance device. Throughout the narrative, his key relationships include his partnership with Tanaka, his protective yet distant bond with the child pilots, and his hostile encounters with Koemushi.