On her way home amidst the approaching typhoon, Satori Yamagami (山神 覚) gets caught up in an incident involving the collapse of a tunnel.
When she awakens inside the bus, she finds that a mysterious entity called "the devil" is standing before her.
Then, a notification appears on her smartphone from the devil, asking her to make a contract to survive. It reads, "This place is now an 'otherworld,' and if you want to live, you must make a contract with me."
Facing a sudden and bizarre reality, the girl agrees to the contract and forms a pact with the devil.
This is the beginning of a strange and mysterious tale of a young girl, Yamagami Satori.