If you’ve seen the anime… the manga is better.
Manga
Orange (Manga) Review
If you knew the past and could use that knowledge to make a better future, would you be able to do it? That’s the question Naho Takamiya is faced with when she receives a detailed letter from her future self with instructions on how to save a boy she hasn’t even met yet. That boy, Kakeru Naruse, is the boy Naho will fall in love with and the boy who will eventually break her heart when he’s killed in a car accident on his 17th birthday. But the present Naho has been given an opportunity to avoid this future of regrets, guided by the letter in the ways she can save Kakeru.