Hello World: The Manga

Naomi is a shy teenage boy living an ordinary life until the day a mysterious man appears -- himself, from ten years in the future. Future Naomi brings a dire warning: Naomi's soon-to-be-girlfriend Ruri will be in a tragic accident not long after they start dating. Can they change the past and build a better future... or is there something more to Naomi's mission than saving one girl's life?