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.

Mihoshi has been bothering Saku too much lately so he takes a break from the club and goes to the library where he meets the student council president Fumie Kotozuka by chance. After talking with her, Saku realizes Mihoshi is merely expressing her feelings honestly like she always has and Saku agrees to accompany her with stargazing. However, the rainy season begins causing Mihoshi to get very depressed over the cloudy skies. With Saku's suggestion, the astronomy club goes to the planetarium and are shown the summer constellations. After the rain ends, Mihoshi wants the club to go on a summer stargazing camp.

Fumie finds the astronomy club members sleeping in the same room after they collapsed from exhaustion the previous night, and she forbids them from taking part in club activities for one night. The next day, three guys hit on Hime and two literature club members, and Fumie tries to interfere at first, but when Saku goes to help, he trips and falls into the guy's fist. Mihoshi and Hime manage to take care of the three guys, and Saku is taken inside and cared for, though he only has a small cut. While the other astronomy club members are taking a bath, Fumie talks with Saku about the astronomy club's activities and they decide to invite the literature club members the next night to show them what the astronomy club does at night. Hime takes care of pointing out several constellations and the Milky Way, and everyone enjoys the night of stargazing.

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.

Mihoshi and the other members are excited about the Autumn Stargazing Conference, and are surprised at the size of Nogishiro High School along with the number of members in their astronomy club. After the sun sets, everyone splits into groups and the process is explained by Nogishiro's astronomy club president Ayumi Ōmi; each group is free to stargaze until the moon sets, upon which each group will begin counting visible stars in a patch of sky to measure the overall brightness of the sky. Ayumi asks Saku to help on patrol around the school and they come across Hime and a second-year named Musa after she overreacts and thought he was trying to assault her. Afterwards, everyone goes back to the roof now that the moon has has set, and Ayumi confesses to Saku that her astronomy club actually only has nine members in it and mostly everyone else is from other clubs. Takeyasu Roma does a narration of the autumn sky myth which everyone loves. Ayumi later confronts Roma and reminds him that they were once members of the same astronomy club at Goshima Science Museum.