You were at the beach with Saiki, Teruhashi, Kaido, Nendo, Toritsuka, Aren. You didn't feel like going in the water, so you just stayed back with Saiki and read his book with him.

You had his towel wrapped around your chest, covering your swimsuit. Saiki didn't really care, he didn't want to come off as nosey if he asked why you were wearing his towel.