Captain Kaoru Yamamoto, director of Yamamoto Anshin Travel (YAT) and captain of the YAT Dove spacecraft, once operated as the feared space pirate "the old wolf of space." He retired from piracy to establish his tourism agency. Fifteen years before the series, Ann Marigold betrayed him by stealing prototype dimensional tunnel technology to found rival company "Gentleman of the Cosmos," creating lasting animosity.

Ambitious yet frugal, Yamamoto organizes low-cost tours to financially unstable destinations while maintaining a gruff, self-centered demeanor. He harbors deep devotion to his adopted daughter Katsura, whom he raised from infancy after her arrival from destroyed Planet Noah. Founding YAT partially aimed to locate her biological parents.

Throughout YAT’s first season, he navigates constant financial struggles and workplace hazards from outdated technology. His management includes withholding pay and verbal outbursts, yet he retains employee loyalty. Past connections resurface when he manipulates former crewmate Captain Rock into pursuing treasure for later seizure.

A pivotal development occurs when consuming an alien fruit transforms him temporarily into a woman, requiring Goro Hoshiwatari’s kiss to reverse the effect—contrasting his stern authority with vulnerability.

In the second season, set six months later, Yamamoto and his crew are transported to a distant universe by Professor Note’s experimental teleportation device. After the professor’s kidnapping by Emperor Ganon, Yamamoto succumbs to dark influences and joins Ganon’s forces. The crew rescues both, enabling their return to Earth.

His pragmatic, occasionally unscrupulous practices—like misleading customers about tours—clash with moral integrity, exemplified when saving rival Ann Marigold’s daughter Kanea from drowning.