Kazuki Tsuchiya, a second-year Kotesashi High student, takes the field as center fielder for the baseball team. His junior high baseball experience ended when the rigid, competitive club environment overwhelmed him, leading to quitting. Retreating into fictional baseball through games and anime, he nurtured his love for the sport within otaku culture.

Shy and introverted, Kazuki often hesitates under pressure but openly embraces gaming, anime, and occult interests. He champions otaku communities as egalitarian spaces and views reality through a two-dimensional lens—comparing teammate Kei Kaname's amnesia to an anime plot or dubbing Kei's strategic focus "Chishou" mode. He addresses Kei as "Kei-sama" with earnest admiration.

As a right-handed player wearing jersey number 8, Kazuki lacks physical strength but boasts speed nearly matching teammate Shunpei Chihaya. This makes him pivotal for disruptive tactics like double steals, though he bats ninth due to limited hitting power. His defensive skills and stamina steadily improve, and he wields a no-brand discount-store glove, reflecting pragmatism.

Kei and Shunpei's persistent recruitment overcame Kazuki's reluctance rooted in past discomfort. Their recognition of his speed gradually convinced him to join. During a critical game against Teitoku High, he executed a double steal with Shunpei, their combined speed creating a scoring opportunity and cementing his role. Teammate encouragement fuels his growing confidence.

Kazuki lives with his parents in a standard family setting. His image color is purple. He stands 169 cm tall, has blood type A, and was born on November 17 under the Scorpio sign.