Yukinari Sasaki has been bullied by girls ever since he was young. Now that he's a high school student, Yukinari has developed gynaphobia - a severe allergic reaction to girls. Whenever a girl gets close or even talks to him, he breaks out in hives. But changes are in store for Yukinari when an altercation with his neighbour and childhood friend Kirie Kojima knocks him through a portal that connects his bath with the bath of Miharu Sena Kanaka - a girl from the world of Seiren. He is surprised when he does not break out or get nervous when she gets close.