Without fail, whenever a Manga/Anime character goes to a festival and wears a Yukata for the first time, they will injure themselves on the traditional Japanese slippers they wear. I don't know that they make those sandals out of but I've never known anyone to hurt their feet on sandals, flip flops, shower shoes, thongs, chanclas, or whatever.
It's as big a trope as being caught out in the rain and catching a cold or just being randomly frail and sickly.