In an upcoming era where human beings have already journeyed to Mars safely, the space program is now aiming to reach Jupiter for the very first time in history. Amami Kosei, one of the elite astronauts on the Jupitonia crew heading towards Jupiter, has been a cherished friend and admired role model to Subaru Yuuto for many years. However, an unforeseen tragedy suddenly ensues, causing a malfunction that leads to an explosion on board the ship, resulting in Jupitonia being lost in deep space with many believing the crew to have perished.
Although he is distraught over the loss of a dear friend and hero, Yuuto enrolls at the Core Space Academy, aspiring to become a super-class astronaut (also known as Sirius) like Kosei was and discovering uncharted regions of the universe. In order to follow in his hero's footsteps, Yuuto must strive to be the best of the best amidst fierce competition. Despite the vast unknown that lies ahead, he must learn to confront his fears as he prepares to become a hero for future generations.
