平行世界·爱情故事是一部爱情片，敦贺崇史与挚友智彦均从事脑科学前沿研究，十余年来情同手足。一日，智彦向他隆重介绍新结识的女友麻由子。他赫然发现，那竟是自己曾一见钟情但失之交臂的女子。 崇史心中爱恨交织，被嫉妒与自责折磨得濒临崩溃。然而，一夕之间，麻由子竟已理所应当般和他生活在一起，并绝口不提智彦，原本致力人脑记忆研究的智彦也下落不明。 崇史被巨大的不安紧紧攫住……
"A world" - After graduating from a university, close friends Takashi Tsurug and Tomohiko Miwa begin work at a company which does brain research. One day, Tomohiko introduces Mayuko Tsuno as his girlfriend. Takashi is stunned. When he was a university student, Takashi saw Mayuko Tsuno every day on the train opposite from the one he rode. He became attracted to her back then. "B world" - When Takashi Tsurug wakes up, his girlfriend Mayuko Tsuno makes breakfast as usual at his apartment. His friend Tomohiko Miwa introduced him to Mayuko and they have lived happily as a couple. Everything seems to be going smoothly, but Takashi begins to have doubts. Tomohiko, who worked with him at the same company, disappears and he can't discern if his memory is real or imaginary.