Gengo Matsunaga serves as the protagonist of the story and was once renowned as the greatest firefighting samurai in all of Edo, celebrated under the legendary title of the Fire-Eating Bird. He is a man of striking appearance, an adult with black eyes and chin-length black hair often tied back in a ponytail, typically dressed in a haori and leg warmers suitable for his dangerous profession.

When the narrative begins, Gengo has already resigned from the fire brigade and is living a quiet, retired life in the rustic countryside alongside his clever wife, Miyuki. However, his peaceful existence is interrupted when he receives an unexpected invitation to serve the Shinjo clan by leading their firefighting team, a unit that has collapsed and is perceived by others as having no money, no personnel, and little worth. Initially hesitant, it is the encouragement of his astute wife that ultimately persuades Gengo to accept this daunting challenge, and he commits to rebuilding the broken team as its chairman. They are ridiculed by others, who mock them as the ragged steeplejacks, but Gengo and his recruits, each of whom possesses their own peculiarities, are determined to struggle and fight for their core mission of saving any life.

A primary motivation for Gengo is the trauma he carries from his past. He walked away from firefighting following a traumatic fire, and a review of the premiere episode suggests he knows at least two people who did not survive it, including his mentor and very likely his father. This history has left a deep psychological scar; when faced with a blaze, his hand begins to shake, betraying a fear that he may no longer have the heart for the work he was once the best at, even though his skills and knowledge remain intact. This internal conflict between his past glory and his present trauma forms a compelling core of his character. Despite this, he is drawn back into the world of firefighting, and it becomes clear he is the only man capable of whipping a group of hapless trainees into shape. Even in retirement, his instincts remain sharp, as he can still pinpoint the sound of a fire bell from a great distance.

Gengo has a significant and supportive relationship with his wife, Miyuki, whose encouragement is the catalyst for his return to duty. He also develops key relationships as the leader of the Boro Tobi Gumi, the rag-tag fire brigade he is tasked with rebuilding, forming bonds with its members, which include a mood-maker vice-president, a kind-hearted former sumo wrestler, and a skilled military strategist. His primary duty in the story is to lead this disrespected and underfunded group while contending with a growing mystery, as Edo is plagued by a series of suspicious fires, potentially set by an elusive arsonist known as Foxfire.

Gengo possesses several notable abilities that set him apart. His legendary status as a fire-slayer speaks to his immense bravery and prowess in the face of one of history's most destructive forces. He also demonstrates a remarkable, almost psychic ability to detect the presence of humans trapped within the belly of a fiery blaze, which is what originally characterized him as a true hero. This ability allows him to calculate danger and dive into infernos where modern equipment does not exist, making him an invaluable force in his life-saving mission.