The letter from the future details the regret felt by everyone for being unable to celebrate Kakeru's birthday. As such, high school Naho and the gang pester Kakeru about what he wants until the big day. On the other hand, 26 year-old Naho and the gang gather at the late Kakeru's grandmother's house to celebrate his birthday, like they had promised in the past.
Sorry we didn't notice before.
.آسفة لعدم ملاحظتنا من قبل
Tut mir leid, dass ich das
nicht vorher gemerkt habe.
Perdón por no habernos dado cuenta.
Perdón por no habernos dado cuenta.
Excuse-nous 
de ne pas l’avoir remarqué.
Scusaci se non ce ne siamo accorte prima.
Sentimos muito por não termos percebido.
Прости, что не заметили этого раньше.