Aoki is a character from the Paldea region who serves a dual role within that area's Pokémon League. He holds the position of both the Gym Leader of Medali City and a member of Paldea's Elite Four, a unique arrangement assigned to him by the league's chairwoman, Geeta. In his duties as a Gym Leader, Aoki specializes in using Normal-type Pokémon, which he feels reflect his ordinary and unassuming image. For his Elite Four responsibilities, however, he is required to use Flying-type Pokémon, a directive that comes from Geeta and is a source of personal dismay for him.

Aoki is a serious and brooding middle-aged man of average build. His appearance is notably generic, befitting his reputation as an exceptional everyman, though his face features prominent cheekbones and square-shaped grey eyes and eyebrows. He consistently wears a light black business suit with a grey shirt and a pale blue tie patterned with clouds, which references his Flying-type specialization. He is also always seen carrying a black briefcase.

In terms of personality, Aoki is characterized by a lack of motivation and a very serious, businesslike demeanor. He is a hardworking businessman on top of his League duties, and his demanding schedule leaves him perpetually overworked and tired. One of his most distinctive traits is a tendency to become completely still when lost in thought, a habit that often worries the people around him. Despite his weary exterior, he has a notable fixation on food and regularly dines at the Treasure Eatery in Medali, which also serves as the arena for his Gym battles.

In Pokémon Horizons: The Series, Aoki appears as an examiner for the students of Orange Academy during their Terastal training in the Paldea region. His role in the story is to act as a formidable and strategic opponent who tests the growth and adaptability of the young trainers. He is first seen alongside the other Paldea Elite Four members at the academy.

A key relationship is formed with the student Dot, who faces him for her second practical test. During their battle at the Treasure Eatery in Medali, Aoki serves as a calm and analytical foil to Dot. He consistently stays one step ahead of her plans, forcing her to think more creatively and work in true synergy with her Pokémon. He shows no outward aggression but is a precise and relentless battler, offering a clear measure of Dot's progress.

The battle with Dot also provides a moment of development for Aoki as an examiner. Rather than simply defeating his student, he evaluates her performance on multiple criteria. He acknowledges not just her tactical shifts and use of Terastal phenomenon, but also her ability to adapt to her Pokémon's spontaneous ideas. He ultimately passes her despite her loss, demonstrating that his role is to foster growth rather than just secure victory.

Aoki's notable abilities as a trainer are considerable. He is a member of the Elite Four, placing him among the most powerful trainers in Paldea. In his battle against Dot, he demonstrates a highly strategic and adaptive battle style, using moves like Glare to cause paralysis and controlling the flow of the fight. He is also proficient in using the Terastal phenomenon, capable of Terastallizing his own Pokémon to gain a decisive advantage. His calm and experienced presence in battle makes him a significant obstacle for any challenger.