Mitsuya Saida is a twelve-year-old normal-ranked Bottle Battler and a close friend of Kouta Kouga since childhood. His name is derived from Mitsuya Cider, a Japanese brand of carbonated drink. He first met Kouta after facing rejection from other peers, and Kouta encouraged his passion for Bottle Battling, forming a lasting bond. Mitsuya is a serious Bottle Battler enthusiast and a huge fan of the fighter known as Citrus. He is characterized by strategic and careful gameplay, though he occasionally displays cockiness during matches. Initially using a generic Bottleman with a Mitsuya Cider-inspired design, he later acquires Arrowcider DX, a control-type Bottleman, after intensive training. In the story, Mitsuya supports Kouta as a fellow battler and friend, often practicing alongside him and contributing to the group's efforts in tournaments and battles. His role is that of a reliable ally who brings technical knowledge and a steady approach to the team. His development revolves around honing his skills and obtaining a more advanced Bottleman, reflecting his dedication to the sport.