First-year middle-school student Yuki Mizuhashi is troubled by a vision of a girl falling headfirst at the same time every day. With a red contract and the help of Seira Akemiya, who calls herself a supernatural-phenomena consultant, Yuki confronts the unsettling events lurking at school.

For those who sign the red contract, Seira's advice and binding instructions point the way out of supernatural danger.

Hotaru Aoki, a first-year middle-school student, has hidden a love letter to her childhood friend Hayate in her desk drawer. Then she hears the same words from her lost letter in a song uploaded by a mysterious singer named Luca. Matsukaze Hikaru, the feared head of the disciplinary committee, reveals Luca's identity and asks Hotaru to continue writing the letter.

The words of a lost love letter have become a mysterious singer's song.