A woman in Luwan and Konoha Special Decryption Organization (whose name I can't remember, but she has feelings for Luwan) asked Iruka, Kakashi and others didn't know, so she had to ask Naruto. When Naruto saw the first word like 9 (Lu Wan thought so), she remembered that she had written the same word when she saw Jiraiya writing a book. At first, she felt like 9 years old when watching Naruto, but Jiraiya said it was his writing habit. After he knew it, he wrote the same word.