Nobuhiko Otoi, grandson of robotics expert Professor Shinnosuke Otoi, resides permanently with his grandfather in Tokkari Town due to his parents' robotics research abroad. During the development of the combat robot Signal—designed as Nobuhiko's protective older brother—an accidental sneeze corrupted the programming. This glitch forces Signal to transform into a hyperactive, chocolate-obsessed toddler-sized version ("Chibi Signal") whenever Nobuhiko sneezes. Subsequent sneezes revert Chibi Signal to his original form.

Nobuhiko repurposes this flaw as a tactical defense. He intentionally triggers sneezes to summon Chibi Signal during combat, specifically to dodge assaults from Pulse, Signal's weaponized prototype. The strategy leverages Chibi Signal's compact size and erratic behavior for battlefield advantages.

Signal's programmed duty evolves into authentic brotherly loyalty. He instinctively safeguards Nobuhiko beyond combat protocols during conflicts. Nobuhiko actively assists Signal in missions, aiding directly against threats. Their partnership hinges on mutual dependence, with Nobuhiko’s decisions critically shaping Signal’s combat efficacy.

A projected sequel, *Twin Signal Biennial*, would depict Nobuhiko at age thirteen, confirming narrative continuity. Signal and other established characters appear in this concept, though specifics of Nobuhiko's growth remain unrealized pending the project's crowdfunding outcome.