Brago is a mamodo, a supernatural child from another world, who participates in the battle to determine the next ruler of the mamodo realm. He is fourteen years old and has a gothic appearance, characterized by his short stature, athletic build, pale skin, and black hair and eyes. He typically wears a large fur coat and black boots, and has distinct tattoos on his arms. His expression is often stern or menacing, and he has a mouth with small fangs.

Initially, Brago possesses a vicious, heartless, and aggressive personality. He resents weakness, both in others and in himself, and is particularly frustrated by his reliance on a human partner to fight. He is extremely antisocial, rarely interacting with other mamodos, and many of them fear him due to his immense strength and reputation. In the early stages of his partnership with Sherry Belmont, he is often cruel, threatening her and her loved ones to push her to discard what he sees as useless sympathy, believing that only by being ruthless can they unlock the power needed to win the battle.

Brago's primary motivation is to become the powerful and strong king of the mamodo world. However, his ambition evolves over time. He begins with a desire for power for its own sake, but he eventually aspires to be a strict yet benevolent ruler, expressing a wish to deal with villains using his own strength rather than relying on the King's Privilege, a special power of the king. His secondary, but deeply significant, motivation becomes helping his partner, Sherry, rescue her friend Koko from the control of an evil mamodo named Zofis.

Brago serves as one of the primary rivals to the protagonists, Zatch and Kiyo. He and Sherry are one of the most powerful teams in the battle, having burned more spellbooks than almost any other pair. Their role in the story is often that of a formidable force that even the main characters must strive to overcome. They are not strictly villains but act as anti-heroes, pursuing their own goals of winning the battle and saving Sherry's friend, which sometimes aligns them with the protagonists against a common, greater threat.

The most significant relationship in Brago's life is with his bookkeeper, Sherry Belmont. Their partnership begins with conflict and mutual distrust. Brago sees Sherry as weak, and Sherry is horrified by Brago's brutality. The turning point in their relationship occurs when Sherry threatens to kill herself, which would prevent Brago from becoming king, forcing him to submit to her will. Over time, as they travel and fight together, this forced alliance develops into a deep bond of mutual respect and care. Brago trains Sherry to become a capable fighter, and while he continues to criticize her weakness, his actions often reveal a protective nature. Sherry, in turn, vows to make Brago king after he helps her save Koko. In their final battle, when defeat is imminent, Brago gently takes Sherry's hand, thanking her for being his partner and expressing that he was happy to have had her by his side.

Brago undergoes significant character development throughout the story. He transforms from a selfish, borderline psychotic fighter who only values power into a more noble and compassionate individual. He learns to care for his human partner and, by extension, the feelings of others. This is demonstrated when he offers words of encouragement to a human child, telling him to become strong so he doesn't have to suffer. He also learns to cooperate with others, including his rivals Zatch and Kiyo, setting aside his pride to work as a team against a powerful enemy. By the end of the battle, he acknowledges Zatch's strength without resentment and fights not just to win, but for the sake of the thrilling challenge and the bond he has formed.

Brago's notable abilities center on the power to manipulate gravity. He is incredibly strong even without using spells, capable of destroying a bulldozer or shattering large boulders with a single punch. His spells, which are activated by Sherry reading from his spellbook, allow him to perform a wide range of gravity-based attacks. His most basic spell, Reis, fires a small ball of gravity. More powerful versions include Gigano Reis and Dioga Gravidon, which can destroy a mountain. Other spells like Gravirei create powerful gravitational fields that pin opponents to the ground, while Ion Gravirei fires a devastating beam of gravity. His ultimate spell, Shin Baberuga Gravidon, is immensely powerful, capable of halting the Earth's rotation for a short time by tapping into the planet's magnetic fields. Using his powers puts a great strain on his body, especially if he draws in too much of the planet's energy.