Manabu "Gaku" Taira narrates the story, recounting his journey as co-founder of Trillion Game from his perspective. Initially reclusive, timid, and socially awkward, he stands in stark contrast to his business partner Haru Tennoji. His core technical expertise in computer programming and hacking surfaces when he unintentionally reveals his ability to breach Dragon Bank Enterprises' security systems during a job interview, an act capturing Kirika Kokuryu's attention.

Haru first encounters Gaku while intervening to stop him from being bullied. This meeting leads Haru to recognize Gaku's technological talents, forging their partnership. Despite his weak-willed nature, Gaku possesses exceptional self-taught programming abilities rivaling professionals. His nickname "Gaku" originates from the on'yomi reading of "Manabu."

Throughout their ventures, Gaku operates behind the scenes, handling technical development while relying on Haru's charisma for external negotiations. He deeply values a ¥200,000 office chair, purchased by Haru with their initial startup funds, symbolizing their early partnership. As Trillion Game evolves from startup to major corporation, Gaku significantly develops, transitioning from a supporting technical role to becoming the company's President in the present timeline.

In the live-action film continuation, Gaku faces new challenges as Trillion Game ventures into developing Japan's first casino resort. This storyline tests his leadership capabilities and the durability of his partnership with Haru when confronted by a conspiracy threatening their company and friendship. Kazuma Kokuryu's manipulation tactics create tension between the co-founders, forcing Gaku to operate independently during Haru's unexplained absence. His character arc culminates in his emergence as a decisive leader capable of steering the company through high-stakes corporate battles and upholding Trillion Game's vision amid complex power dynamics.