At the end of Love Letter, why did Fujii Iki not tell Watanabe about the portrait on the back of the library card?

Answer 1

At the end of Love Letter, Fujii Kazuki didn't tell Watanabe Hiroko that the portrait on the back of the library card was him because he had mistakenly written another person's name on the portrait when he was writing the love letter. He realized that he had made a mistake, but it was too late because he had fallen in love with someone else when he wrote the love letter, and that person also loved him. In order to avoid letting Watanabe find out his true feelings, he didn't tell her that the portrait on the back of the library card was him.