A 2018 water-park OVA bundled with the manga's ninth volume. At the pool with friends Nakai and Mano, Takagi challenges Nishikata to catch up to her on the big slide, then unnerves him with a rumor that couples who ride it together fall in love, sending the flustered boy crashing to the bottom. A short post-credits scene closes the playful day on the bus ride home.