After having moved away several years earlier, Saku Öyagi 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...