After having moved away several years earlier, Saku Oyagi returns to his hometown to begin his high school life. Saku has always enjoyed simply staying home and reading books, but his childhood friend Mihoshi Akeno used to forcibly take him outside to take part in various activities. On their last day together, Mihoshi fell out of a tree, causing Saku to go to the hospital with a broken arm, and since then Saku has never wanted to see Mihoshi again. However on his first day at high school, he meets Mihoshi as she is trying to recruit members into the astronomy club. Saku attempts to avoid her as well he can, but after Saku realizes that the reason Mihoshi did not see him off years ago was because she too was in the hospital, Saku makes up with Mihoshi, and joins the astronomy club.

No one besides Saku has joined the astronomy club, so recruiting tactics are still going on. Hime Makita from Saku's class is annoyed that Mihoshi and other astronomy members come to their class so often when she would rather spend some time alone with Saku. Hime met him on the bus to take the entrance exam of the school they now attend, and was thrilled to see they were put in the same class. After Hime finds out that Saku and Mihoshi are not dating, Hime joins the astronomy club, which finally becomes officially recognized. Another day, the astronomy club members go stargazing far from the city's lights.

The new semester starts and on the bus to school Saku notices a tall man also getting off at the school. During the welcome back ceremony, the man that Saku saw earlier is introduced as a new teacher named Nozomu Soma who is in charge of Saku's class and world history. Mihoshi calls him "So-nii" in front of everyone and rumors abound as to what their relationship is. Later, Soma becomes the astronomy club's adviser and he explains to the others how Mihoshi's father was his professor at college and also the club adviser for their astronomy club. Soma wants the club to do a planetarium for the upcoming cultural festival and they get in the top three in a popularity contest in exhibits, the club will get more funding. Saku becomes annoyed at Mihoshi's and Soma's relationship and is approached by Fumie to help with the literature club.

Despite initially going to refuse, Saku ends up agreeing to help the literature club. Mihoshi acts cheerful without him there, but is still troubled by his absence. Meanwhile, the astronomy club has their hands full with making the planetarium. Mihoshi suddenly hugs Saku one day after school and rumors spread after some athletic club members see them together with Soma. Fumie becomes concerned that Saku has been helping the literature club too much and that he may be concerned about the rumors regarding him, Mihoshi and Soma. Hime gives Saku a journal she compiled about the planetarium's construction. Saku feels re-energized about the astronomy club and goes back to help.

The cultural festival begins, though initially no one is coming to see the planetarium. After Haruko from the city planetarium arrives, she helps to bring in the people and the planetarium is well received by viewers for the rest of the day. Mihoshi thanks Saku for everything he has done for the club and is thankful that she has not caused him any trouble while he was helping the literature club. After the festival, the club members are distraught at the thought of dismantling the planetarium, but eventually take it down. The astronomy club was not able to win any prizes for the festival and thus still do not have enough money to even buy a telescope. Sayo takes the club to her family's Buddhist temple and perform a small moon festival. The astronomy club receives a video letter from the president of the astronomy club of Nogishiro High School in the same prefecture as Sōei High School inviting the club to the Autumn Stargazing Conference of the Prefectural High School Astronomy Network.

After overhearing Mihoshi and Soma about plans together on the weekend, Saku, Hime and Edogawa follow them around town to find out what is going on, and initially they are out on a date. They eventually follow them to the grave site of Mihoshi's father who died in a car accident and everyone pays their respects. Saku, Hime and Edogawa feel awkward around Mihoshi after this. Fumie tries to give Saku a bookmark souvenir from her school trip to Hokkaido, but her glasses are broken after Saku protects her from a stray baseball. Saku offers to walks her home and on the way they run into two members of the literature club who to take her the rest of the way. Saku gets Fumie's help to set up a shooting star viewing event at school for Mihoshi, who is overcome with emotion over it.