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.

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.

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.