Kenkou Zenrakei Suieibu Umishou S01 E07 Curse

There's only one week left until the Prefectural swim tournament. But there's a problem; Amuro has lost one of the "X"s she wears on her head. Given to her by her grandmother, Amuro was warned that she was to wear them all the time and Amuro would be cursed if they were lost.