HELLO WORLD: The Manga 

Naomi, a shy teenage bookworm, is visited by his future self and tasked with fixing his biggest regret–his classmate and soon-to-be-girlfriend Ruri is going to die from an accident soon after they begin dating. But his chance to alter the future soon turns out to be far more complicated, as the very world the teens live in isn’t quite what it seems. (Source: Seven Seas Entertainment)