Saita Mitsuya appears in the series as a child with green eyes and neck-length blue hair, often wearing a bandana. His name originates from the Mitsuya Cider beverage brand. Mitsuya belongs to the main character's friend group and actively participates in their Bottleman practice sessions.

Initially equipped with a generic Mitsuya Cider-themed Bottleman unit, Mitsuya later acquires the specialized Arrowcider DX during a Fan Appreciation Day event, overcoming previous financial constraints. This unit boasts a white base with green stripes, red accents, blue grips, and rhinoceros-shaped Star Beast Armor. Arrowcider DX features multiple operational modes: Grip Mode for stability, Stabilizer Mode for positional control, Barrel Mode for shooting precision, and a power-enhancing Tri-Arrow Mode. Its special moves are Cider Impact and Cider Impact Tri-Arrow.

Mitsuya demonstrates significant development in his Bottleman skills. He initially expresses frustration at the performance gap between himself and his friend Cota. After obtaining Arrowcider DX, he diligently studies tutorial videos to master its capabilities. This dedication results in a victory against the battler Kaori in a control-type Bottle Battle, where he effectively counters her attacks using Stabilizer Mode. His growing proficiency with Arrowcider DX reinforces his commitment to the sport, leading him to challenge Cota following the battle.

His interactions occur primarily within his friend circle during practice and public Bottleman events. A spin-off web series exists, but specific details regarding Mitsuya's involvement or developments within it are not provided.