In the early 21st century, Japan launches its first human spaceflight mission, the Shishigō (獅子号, "The Lion"), near the town of Yuigahama. Grade schooler Asumi Kamogawa witnesses the launch with her mother and classmate Shinnosuke Fuchūya, but the Shishigō explodes moments after liftoff. Ten years later, Asumi and Fuchūya enter the Tokyo Aerospace School. While admiring an astronaut suit on display, the two meet fellow student Kei Ōmi, who remembers Asumi from the entrance examination interview. Takahito Sano, their teacher, opens the first class with an astrophysics lesson and tells the students that he will not wait for those who cannot keep up. Asumi, Fuchūya, and Kei meet classmates Shū Suzuki and Marika Ukita, both of whom received the highest scores in the entrance examination. Asumi also meets a man whose hobby is launching water rockets. During a tour of the school's training facilities, the students are introduced to astronaut and supporting instructor Ryōko Haijima. Kei begins to act cold toward Asumi when she finds out that Asumi's father worked as a former engineer with Ms. Haijima, suspecting that Asumi was accepted at the school due to her connections. Asumi remembers her father's decision to pay for her tuition despite disapproving Asumi's entrance into the school. The students are separated into groups for a team assignment the following day, and Asumi is assigned to the same group as Fuchūya, Kei, Shū, and Marika. Shū assumes leadership of the group while Marika distrusts her teammates' judgments, causing a conflict with Kei. The team completes the assignment in time for the deadline, but they are given a final test to remember the room number they were assigned too. Asumi is the only one in the group who remembers because their room number is the distance to her favorite star, Spica. After the training, Kei apologizes to Asumi for thinking of her badly. Asumi remembers her father telling her as a child that her mother became a star when remnants of the Shishigō fell on Yuigahama and killed her. She promised to become an astronaut so that the two can go to space to meet her mother again. One day, Mr. Sano tells Asumi that she will never be allowed in space because her father caused the Shishigō accident.