Haru Tennoji is a central protagonist of Trillion Game, a charismatic and ambitious young entrepreneur who proudly declares himself the world's most selfish man. He is easily recognized by his long, flowing hair and a flashy, rebellious style of dress that matches his bold and carefree personality. One of his most distinctive traits is his laugh, which is often transcribed as "KuHAHA" or in some adaptations as a hearty "Ha Ha Ha," reflecting his boundless confidence and enjoyment of a challenge.

Regarding his background, Haru grew up in Tottori, where his family runs a sushi restaurant called Sushi Tennoji, with his father working as a chef there. His mother passed away when he was young, a fact that adds a layer of depth to his otherwise exuberant character. Despite his gregarious nature, much of his personal history remains deliberately mysterious, which only adds to his enigmatic charm.

Haru possesses an extraordinary range of abilities that he uses to pursue his goals. He is a genius communicator and negotiator, capable of charming or persuading almost anyone he meets. His linguistic prowess is significant, as he is fluent in multiple languages, including English, Chinese, and French, which he uses to his advantage in high-stakes business negotiations. Beyond his social skills, he is also depicted as being highly intelligent and possessing considerable physical strength, making him capable of handling himself in confrontational situations. His strategic mind is ruthless and creative; he is willing to use any means necessary to win, including deception, bribery, and even breaking the law, all in the service of his ultimate ambition.

Haru's central motivation is a remarkably audacious one: to earn one trillion dollars and build an unrivaled business empire from the ground up. To achieve this, he co-founds the company Trillion Game, where he takes on the crucial roles of public face, sales representative, and primary business decision-maker. His defining role in the story is as the visionary and driving force behind this startup, constantly generating outlandish plans and leveraging his social genius to open doors that would otherwise remain closed.

His most significant relationship is with his childhood friend and business partner, Manabu Gaku Taira, an introverted but exceptionally skilled computer engineer. Their partnership is the heart of Trillion Game; Haru provides the salesmanship and strategy, while Gaku provides the technical expertise. Haru has an unwavering belief in Gaku's abilities, a loyalty that is powerfully demonstrated when he quits a highly sought-after position at the nation's largest IT company, Dragon Bank, on his very first day simply because they had rejected Gaku's job application. He is known to go to great lengths for his friend, even selling his personal watch to finance Gaku's entry into a hacking competition. While Haru acts as the front man, he is also a skilled supporter behind the scenes, indicating that his selfish persona masks a deep dedication to the collective success of his team.

Throughout the story, Haru remains a constant force of audacious action. He turns down the prestigious Dragon Bank job to start his own venture with Gaku, securing investment from a venture capitalist by sheer force of will. As the narrative progresses, especially in live-action adaptations, his methods become increasingly extreme. When the company is threatened, he engages in insider trading, blackmail, and other morally questionable activities to protect his friends and their dream, actions that ultimately paint a target on his back and force him to disappear for a period of two years to shield the company from repercussions. His development reveals that despite his "world's most selfish" moniker, his most defining traits are his loyalty, his willingness to sacrifice himself for his friends, and his total, if unconventional, commitment to their shared dream of reaching one trillion dollars.