Yaginuma's work prior to serialization introduces readers to Asumi Kamogawa and her mentor, the ghost of a Lion astronaut whom she calls Mr. Lion. Their friendship develops in several short stories in which, throughout her childhood, he nurtures Asumi's interest in space. As her interest and dreams grow, Asumi is often ridiculed by classmates, especially because she immerses herself in books about space and rarely engages in classroom activities. When she decides to apply for admission to the Tokyo Space Academy, her teachers urge her to reconsider because she is below average height. Her friendship with Mr. Lion continues to grow after Asumi successfully enters the academy, and she often consults him during periods of self-doubt.