A family attends the funeral of Misaki, and during the process, Misaki's sister Yuri, is handed the invite to a school reunion.
Yuri goes along to the reunion to tell them her sister has passed, but everyone assumes it is her and she can't bring herself to tell them otherwise.
While there, Kyoshiro Otosaka speaks to her, and gets her number, telling her that he was in love with her (assuming that she is her sister). They start exchanging letters, and it is revealed that he had a relationship with her, before it broke off and she went out with an abusive man, who fathered her daughter Ayumi. Otosoka became a novelist, and wrote a prize winning novel, Misaki, named after her.
He ends up meeting Yuri again, and then finally her daughters who take him to pay respects to Misaki, where Ayumi reveals the letters, and the chapters he would send were a source of support for Misaki during their bad times. Otosaka, who hasn't been able to write since, now feels he can and starts writing again.
Release
It was released in Japan by Toho on January 17, 2020.