Capitão Kaoru Yamamoto is the founder, president, and captain of the small space tour company YAT, which stands for Yamamoto Anshin Travel. He is the commanding officer of the agency's primary vessel, the YAT Dove. Known as an old wolf of space, Yamamoto has a colorful and formidable past as a space pirate who was once widely feared before he retired from that life to start his legitimate business.

In his role as the head of YAT, Yamamoto is portrayed as a highly ambitious and often egoistic individual whose primary motivation is the financial success of his company. He is known for organizing trips to cheap, and sometimes even forbidden, destinations, which he then sells to customers at inflated prices. This stinginess and desire to cut corners often put his crew in complicated or dangerous situations. On a personal level, he frequently bosses around the young protagonist, Goro Hoshiwatari, exploiting him for labor as the ship's mechanic and janitor to pay for damages he caused.

Despite his gruff, grumpy, and apparently selfish exterior, Yamamoto possesses a fundamentally good heart. This is most clearly demonstrated through his relationship with his beloved daughter, Katsura Tenjoin. He is a devoted and protective father, willing to give his life for her. Katsura is his adopted daughter, and his deep care for her is a central aspect of his character, providing a consistent counterpoint to his otherwise cynical business dealings.

Yamamoto's mysterious past is a significant element of the story's background. He shares a mysterious and conflicted history with Ann Marygold, the powerful president of the Gentleman of the Cosmos corporation, which dominates the space travel industry. This unresolved history connects the small YAT company to the most powerful entity in the universe and is a recurring source of intrigue and plot development throughout the series.

The captain is not a combatant in a traditional sense, but his notable abilities stem from his experience and cunning. Having survived as a pirate, he is a shrewd and resourceful leader. He is a skilled navigator of the complex social and economic realities of space travel, using his wits to keep his small business afloat against overwhelming competition. His primary ability, however, is his resilient and ambitious leadership that holds the eclectic YAT crew together, ensuring that despite his personal flaws, the company continues on its adventures through space.