Takeshi Kido is an ordinary Japanese schoolboy living with his family in the Kanto region, near a lake formed by a meteorite. He shares an exceptionally close, lifelong bond with Kentaro Shiratori, a friend born on the exact same day. Their lives change irrevocably when a monstrous entity erupts from the lake, placing them in mortal peril. This crisis summons Kopu, a benevolent being who designates Takeshi and Kentaro as chosen protectors against the evil Goumon. Kopu grants them magical bracelets called Boppus, enabling their transformation into the combined superhero Barom One. To activate this transformation, they physically join hands and activate their bracelets, merging their bodies and consciousnesses into the singular entity Barom One. Within this partnership, Takeshi provides decisive physical strength, contrasting with Kentaro's intellectual approach – a complementary dynamic essential to Barom One's effectiveness. While fused, their individual forms appear as miniature representations within Barom One's eyes, where they retain awareness and collaboratively control the combined entity. Barom One possesses enhanced physical capabilities and wields the versatile Swiss Army weapon Bop, capable of reconfiguring into tools like throwing blades or the vehicle Machroad. Prior to gaining his powers, Takeshi's background was entirely ordinary, with no extraordinary experiences. Following Kopu's intervention, his defining commitment becomes protecting civilians from Goumon's monstrous threats. The narrative centers on his operational partnership with Kentaro; their combined efforts focus solely on neutralizing Goumon's attacks and safeguarding their community, with no depicted evolution in their personal relationship or individual identities beyond this core mission.