The protagonist, a slacker in the swimming club, is constantly being scolded by his childhood friend, Rinka Sano. Rinka is a hard worker with excellent results, while the protagonist is a slacker who somehow manages decent scores. Rinka believes that if the protagonist took things seriously, he could get a recommendation with his grades and they could attend the same university together. After practice one day, Rinka decides to challenge him to a match. If Rinka wins, she wants him to promise to practice seriously. If she loses, she agrees to do whatever he says as the condition.