Kiyoshi Satō, the oldest member of a group of children thrust into an unexpected interplanetary journey, stands apart as a sixth-grader among younger companions. He naturally assumes leadership, defined by a strong sense of responsibility, honesty, trustworthiness, and kindness. These traits earn him the trust of the adults in his life, who assign him supervisory roles like overseeing the younger children during their independent school summer camp, reflecting confidence in his reliability and judgment.

Despite his outwardly capable demeanor, Kiyoshi grapples internally with uncertainty about his future path. He hesitates to pursue personal desires and second-guesses his decisions. His late father's legacy fuels his introspection about potential careers, contributing to a reflective, sometimes introverted nature. A simpler, yet significant, pre-journey wish was his aspiration to see the moon.

Throughout the adventure across alien worlds, Kiyoshi's paramount priority remains the safety and well-being of the younger children. This protective instinct drives his actions consistently, especially during perilous confrontations with hostile forces or while navigating unfamiliar alien environments. His leadership proves crucial in coordinating efforts during critical moments, including the rescue of a captured companion and the climactic showdown against antagonistic forces seeking universal domination.

The extraordinary journey acts as a catalyst for Kiyoshi's significant development. Facing diverse challenges and making weighty decisions helps him gain clarity about his personal goals and aspirations. By the adventure's conclusion, he resolves his earlier uncertainty regarding his future direction. This growth marks a transition toward greater self-assurance and purpose.

Kiyoshi possesses black hair and grey eyes and is Japanese. His portrayal is centered within this singular adventure.