Haruki Mishima (voiced by Takuma Terashima) is a very ordinary first-year high school student. He became interested in swimming because of a picture book called "The Prince of Mermaids" and then joined the school's swimming club. In fact, Haruki has always been secretly in love with a girl named Mashiki Miharu (voiced by Sayaka Kanda), and it was this girl who loves reading who gave him the picture book that changed his fate. Honda Tayu (voiced by Kenichi Suzumura) is a recognized frivolous boy in the class, but in fact, under his frivolous appearance, his personality is very serious. Mihashi Zhenzhu (voiced by Rie Kugimiya) is a standard honor student who grew up in a strict family. Fate made these two people with completely opposite personalities meet. Looking at Zhenzhu's appearance, Honda felt that his inner feelings were constantly throbbing.