Motivated by the belief that he must always lead the way for his younger brother, Mutta Nanba finds inspiration in a childhood promise with his sibling Hibito as they witness a peculiar sight in the night sky. While Hibito pursues his dream of becoming the first Japanese astronaut to land on the moon with NASA, Mutta faces setbacks after losing his job in automotive development. However, a letter from JAXA changes his fortunes, offering him a shot at fulfilling their long-ago pledge by participating in the astronaut selection process. With this unexpected opportunity, Mutta embarks on a challenging journey to space, where destiny seems to align to bring the brothers' childhood vow to fruition.