Banba Choutarou, often called by his nickname Bancho, is a student in the same class as his fellow Gate Keepers Shun and Ruriko. Hailing from Osaka, he was originally a gang leader before being recruited into the team. His recruitment was unique, as he did not initially display any supernatural abilities. It was Shun Ukiya who believed Banba had the eyes of a Gate Keeper, a conviction that led to the young man joining the fight against the Invaders. His background as a former delinquent contributes to his rough-around-the-edges demeanor, but he has a strong sense of honor that he channels into his new role.

Banba possesses a personality that is marked by over-enthusiasm and a tendency to dramatically overreact, particularly when he finds himself the center of attention from girls, which can lead to comedic bouts of tearful joy. He carries the mindset of a samurai, seeing himself as a heroic protector. This worldview leads him to refer to the female members of his team as princesses, with himself as their sworn guardian, especially showing a notable interest in his teammate Kaoru. Despite his boisterous and sometimes comical nature, his core motivation is to be a reliable and strong fighter who can protect his friends and the people of Japan from the threat of the Invaders. He strives to embody the chivalrous ideal of a warrior, even if his execution is often over the top.

Throughout the story, Banba serves as the muscle of the group. Initially, he does not manifest a Gate ability, relying instead on his incredible natural physical strength to pick fights with thugs and engage Invaders. This lack of a conventional power makes him an unconventional recruit, but his loyalty and fighting spirit make him a valuable asset to the A.E.G.I.S. organization. His key relationships are with his teammates, whom he sees as people to be protected. He holds a particular fondness for Kaoru, whom he frequently calls princess, a term that seems to denote both respect and affection. His relationship with Shun is built on trust, as Shun was the one who saw his potential and brought him into the fold.

Banba undergoes significant development as he learns to channel his raw strength into a true Gate Keeper power. For much of the series, he fights with only his physical prowess, but his latent ability, known as the Gate of Close Combat or the Gate of Solid Crush, awakens later in the series. His Gate is associated with the color orange. This ability manifests from his deep desire to protect others, and it is specifically shown activating when his resolve to defend Kaoru from danger triggers a powerful technique known as the Hyper Inner Circle Throw. The awakening of his Gate transforms him from a simple brawler into a formally recognized and powerful warrior, validating Shun's initial belief in him. His notable abilities include his superhuman strength and his unique Gate power focused on close-quarters combat, allowing him to perform devastating throws and grapples on his enemies.