As the older brother, Mutta Nanba feels that it's his responsibility to stay ahead of his brother.
Space Brothers is a story about Mutta Nanba and his younger brother, Hibito. As the older brother, Mutta Nanba feels that it's his responsibility to stay ahead of his brother. Hibito made a promise that he would go to the moon, while Mutta proudly affirmed that he would go to Mars.