Tosaka is a leading member of the arena team "Grancius Fortes". Originally portrayed as a simple thug, who saw nothing wrong with abusing the shock function of Ako, Natsumi and Akira's collars, although this usually earned him a severe beating from the Chief each time. However, he took on a more important role when Negi and Kotarou joined his arena team. As their manager it is Tosaka's duty to arrange fights for the up and coming arena stars and their constant stream of victories have caused him to gain a great deal of respect for the pair. Kotarou has the tendency to call him "Rooster", due to his hairstyle which looks like the comb of a rooster. Recently, during the tournament in Ostia, Tosaka has discovered the truth that Negi has been altering his appearance. Two days before the battle with Rakan, Tosaka confronted Negi about the truth and tried to blackmail Negi into becoming his slave. Afterwards, Ako confronts Tosaka on this matter and requests that he get rid of the evidence at the cost of what little freedom she still had. Tosaka relinquishes the evidence, but does not accept Ako's terms, suggesting that he is somewhat nice at heart. It is later revealed that he was also as slave, and earned his freedom through prize fights with Vargas and "The Chief". Tosaka seems to hold a sort of jealousy towards Negi in the fact that he is on the verge of rescuing Ako and the others in only a month and a half, whereas his freedom took 18 years. Tosaka has also been recently revealed to be a capable fighter, first on the occasion where Ako asks for him to stop blackmailing Negi. When his friends try to take advantage of her conditions (absolute submission, which Tosaka's friends wish to use in a sexual manner), Tosaka begins to emit a very ominous field of magic energy. The second occasion is when Negi tells Tosaka that he cannot win against Rakan. He begins to attack Negi, inflicting many wounds, which causes Negi himself to ponder about his power.