Raibu! (E04)

The sight of Yuu on the beach at night with Koyuki is such a shock to Fuuka that she runs away. Yuu tries to make up for it by explaining that he and Koyuki were friends as kids, but that angers Fuuka even more as she asks why he never told her this before. Yuu's attempt to make up fails, and the mood remains awkward between them at work as well. Then their teacher, Tomomi, shows up at the beach house with the track team captain, Nachi, and Fuuka learns something even more shocking... (Crunchyroll)