A 2018 water-park OVA bundled with the manga's ninth volume. At the pool with Nakai and Mano, Takagi dares Nishikata to catch up to her on the big slide. She then unsettles him with a rumor that couples who ride it together end up falling in love, and the flustered boy goes crashing down to the bottom. A short post-credits scene closes the day out on the bus ride home.