Manabu Taira, who goes by the nickname Gaku, is one of the two central protagonists of Trillion Game. He is a shy and timid individual with a reserved, socially awkward demeanor. Despite his introverted nature, he possesses an extraordinary aptitude for technology and programming, described as a computer genius and a gifted hacker. He has black hair that is cut to ear length, often wears glasses, and is typically seen in formal attire such as a suit.

Gaku’s background begins as an unemployed programmer struggling to find work due to his shyness. His life changes when he reunites with his childhood friend Haru Tennoji, who saves him from a mugging. The two quickly discover that their contrasting personalities complement each other. While Haru is charismatic, bold, and ambitious, Gaku provides the technical expertise and quiet reliability needed to turn their shared dreams into reality. Together, they found the tech company Trillion Game, with Gaku serving as its chief technology officer and later as its president.

Motivated by his deep trust in Haru and a desire to build something meaningful, Gaku uses his exceptional programming and engineering skills to execute Haru’s often audacious business ideas. He is the indispensable technical backbone of the company, responsible for the actual development and security of their products. His role in the story is that of the grounded, analytical counterbalance to Haru’s flamboyant risk-taking, and the narrative unfolds largely through Gaku’s memories, showing his personal growth from a hesitant jobseeker into a confident corporate leader.

Gaku’s key relationship is with Haru, his partner and closest friend. Their dynamic is central to the plot: Haru’s outgoing nature pushes Gaku out of his shell, while Gaku’s technical brilliance gives Haru the means to chase his trillion-dollar goal. Gaku also interacts with other characters such as Kirika Kokuryu, the influential banker who becomes an early investor, but his connection with Haru remains the emotional and strategic core.

Over the course of the story, Gaku undergoes significant development. He grows more assured in his abilities, learns to navigate the business world alongside Haru, and gradually overcomes his social inhibitions. His notable abilities include advanced hacking, software engineering, systems architecture, and a deep understanding of information technology. These skills make him the engine behind Trillion Game’s rise, transforming a startup into a global powerhouse.