mc was a young man, i kinda forgot if he was a college or high school student. He have crush with a girl from his school but does not have courage to confess because he think she was too perfect for him.

After that , mc meet a girl jumping out from pond(not sure of this, my memory kinda vague), the girl then say she was from parallel world, she then say she know mc(but mc did'nt know her) and tell him she and him was best friend in her parallel world.'

the world was exactly the same with 2 different thing, first, it seems the girl did'nt exist in mc world, second, the girl tell mc that he was dating his crush on her pararell world.'

so begin the story of our mc....