It had been Natusya's idea to visit a waterpark when he returned to Japan and of course, Ikuya and Hiyori readily agreed, seeing as the weather had been uncomfortably hot for the past few weeks. And of course, he just had to challenge someone to race him. It was practically a personality trait at this point. Written for the HiyoIku Summer Weekends Event on Tumblr for the prompt 18th July: Water Parks