The End of the World, I Fell in Love With You

Sana Natsukawa is a second year high school girl with a one-sided crush on her childhood friend, Shun. But somehow things just keep getting in the way, and she can never find a chance to talk to him. Suddenly, it seems like fate is finally on Sana's side, as she and Shun become classmates! This is her chance to finally get close to him again! Or so she thinks... when a mysterious boy named Kariya appears before her and stops her in her tracks. "Could it be, a rival in love?!" she wonders, ready to fight it out fair and square. It's then that Kariya shares an unbelievable prophecy to Sana: Shun and she's descendants will destroy the world?!

Source: carbon scans