Okay there's something that is confusing me, the future chnaged right.. Like Noha ended up with kakeru right?…
Ok this is what I understood: the story unfolds in two parallel worlds: "the future", where Naho and Suwa are together but Kakeru is dead, and "the present", where all prevent Kakeru's death, even if it means that Naho and Suwa don't end up together. Although they changed Kakeru's fate in "the present" and apparently he and Naho end up together, he's still dead in "the future" because obviously they can't do anything about it. That's why they decided to write letters for themselves in "the present" 10 years ago, to create a parallel world where they can save him :) hope I haven't confused you more lol