Yuta Agatsuma is a high school student who has no romantic experience. He doesn't know what true love is like, but he finds his classmate Nodoka Kanzaki interesting. Is this love!? Meanwhile, his younger sister Yoru, who dreams of summoning demons, is performing summoning rituals again. This time, the summoning circle suddenly starts to glow, and a girl descends from above. She is Lars, a demon from the underworld, and she offers Yuta a contract!? A thrilling 7-way love comedy begins, where cheating = the end of the world!