This is something I cannot say to your face, so I wrote it in a letter.
When Kazu finished reading, Kohtake and Kei looked up at the ceiling and began to cry loudly. Kohtake understood why Fusagi had handed this letter to her, his wife from the future. From the letter, it was clear that he had guessed what she would do after she found out about his illness. And then, when he came from the future, it became clear to him that, just as he predicted, in the future she was caring for him like a nurse.