Nene Yashiro, a first-year at Kamome Academy, summons the famous ghost of the girls' bathroom — but instead of the rumored Hanako-san, a boy named Hanako-kun appears. After Nene rashly swallows a mermaid scale to win a crush's affection, the curse binds her to Hanako-kun as his assistant, tasked with maintaining balance between the school's Seven Mysteries and the supernatural forces that feed on them.