Motivated by his duty as an older sibling, Mutta Nanba has always felt compelled to stay ahead of his younger brother, Hibito. Consequently, when the brothers witnessed a peculiar occurrence in the night sky back in the summer of 2006, they vowed to pursue careers as astronauts. Hibito set his sights on traveling to the moon while Mutta aspired to explore Mars. Fast forward to 2025 and Hibito is preparing to become the first Japanese person to set foot on the moon while Mutta has been dismissed from his job at an automotive development company. Despite facing challenges in securing alternative employment, Mutta's life changes dramatically when he receives a letter from JAXA, informing him that he has been accepted to participate in the next astronaut selection. It seems fate has presented Mutta with an opportunity to honor the pledge he made to his younger brother all those years ago, and he eagerly embraces the arduous challenge of going to space.