Kiyoshi Satō stands as the oldest in the central group of children, a sixth-grade student. He naturally embodies leadership through a strong sense of responsibility, honesty, trustworthiness, and kindness. However, he often hesitates and wrestles with self-doubt, second-guessing his choices and feeling uncertain about his future. This caution springs from a deep desire to protect the younger children under his watch, prioritizing their safety throughout their journey.

Adults at the summer camp entrust him with supervising the other children, demonstrating their faith in his reliability and maturity. He feels uneasy when others try to assist him, especially if he believes it burdens them, like when his mother offers to cook after work. A significant personal motivation is his long-held wish to see the Moon, a dream fulfilled when Pochi rewards the group with a trip there.

Facing challenges and making critical decisions during the interstellar adventure helps Kiyoshi gradually conquer his indecisiveness. By the journey's end, he gains clearer insight into his personal goals and future direction, resolving his earlier uncertainty.