Taichi Yagami falls in love with Sora Takenouchi.
Unable to confess, he is gifted with by a deus ex machina with Miss Takenouchi's phone number. Never minding the strange area code, he immediately calls her, and is overjoyed to find out that she has a crush on him as well.
But, the next day, when he recounts the previous day's confessions to Sora, she only looks at him with a perplexed expression before giving him the "Friend Zone" speech and revealing she's in a relationship with Yamato Ishida now.
After some investigation, Tachi finds out that the girl he called is not the same girl he fell in love with. In fact, she doesn't exist in this universe at all. She is the girl's alternate universe counterpart, who has fallen in love with the MC's own AU self, who too is blissfully unaware of her crush.
Hijinks ensue as the two strike up a deal to give each other their darkest, most private secrets in order to equip the other with the weapons they need to conquer the heart of their other selves. While the two chase their respective loved ones, DRAMA ensues as they begin to fall in love with each other instead and question the NATURE of NTR.