It’s the spring of Naho’s second year in high school, and Naho receives a letter from herself, 10 years in the future. The letter accurately depicts what’s about to happen, including details on a transfer student from Tokyo, Kakeru Naruse, who ends up sitting beside her in class. On top of that, the letter also begs Naho not to invite Kakeru out with her group of friends on that day alone, but why?

In the letter, it says Kakeru won’t join the soccer club, but in reality, he does. This difference between the letter and reality fills Naho with hope, as she believes it may mean that the future is starting to change for the better. But just as she begins to think that, she has to deal with the letter detailing how Kakeru and Ueda-senpai begin to date...

Naho is so concerned about Kakeru’s date with Ueda-senpai over the holidays, she can’t help but seem preoccupied and unable to focus on her friends’ conversations. Ever since Kakeru started dating Ueda-senpai, Naho has found it difficult to have a proper conversation with him. Naho regrets not directly telling Kakeru how she really felt the day Ueda-senpai asked him out, but what will she do now?

Kakeru gives Naho a hairpin. And on the weekend, Kakeru invites Naho to study with him for the upcoming exams. As the pair begin to grow closer together, Naho gets up the courage to invite Kakeru to see the fireworks together with her at the end of the school festival.

Up until now, Naho had been doing everything the letter from the future had told her to do, but is the letter always right? The letter from the future asks Naho to make sure Kakeru doesn't run the relay race at the athletic festival, but what does Naho decide to do?

It's the athletic festival. Kakeru hurt his ankle during the pole-toppling game, and hid that fact from everyone else. Kakeru tries to keep his suffering to himself, when Suwa and the gang call out to him. Met with everybody's kindness, Kakeru begins to tell them what he's been keeping pent up inside. And then, the class relay begins.

Naho got into a fight with Kakeru on New Year's Eve, and never managed to apologize to him before he passed away. At least, that's what the letter from the future says. However, Naho now believes that she's capable of dealing with whatever may come up, and faces New Year's Eve head-on.

Naho can't give her Valentine's Day chocolate to Kakeru. Ever since what happened on New Year's Eve, Kakeru keeps putting distance between Naho and himself. But, through all the hardships, Naho refuses to give up and fully intends to tell Kakeru how she feels. And so, the time comes for everyone to face the fateful day outlined in the letters from the past, "Kakeru's Final Day."