Following the closing of Uranohoshi Girls' High School, the third-year students—Dia Kurosawa, Kanan Matsuura, and Mari Ohara—have just graduated, leaving Aqours with only first and second-year pupils. While looking for a new practice location for the remaining members, they decide to pay a visit to the new school where they will soon be enrolled. Surprisingly, the structure appears to be abandoned! It turns out that the pupils were sent to a branch school owing to the school board's concerns about how the newly transferred Uranohoshi students would strain the clubs. This gives Aqours a new goal: to demonstrate that Uranohoshi students are also serious about their groups. Meanwhile, another issue has arisen: the third-years have mysteriously vanished on their graduation trip!