I don't have a definite answer. It could be a character involved in a complex situation that led them to lie first. The mystery might only be solved as you delve deeper into the novel.
Mirai Diary was a Japanese light novel written by Ishikawa Mae, which had also been adapted into manga and animation. The story was about the protagonist, a high school student named Dohiko Tanaka, who accidentally obtained a book called "Future Diary". This diary allowed him to predict the changes in the future.
In the future diary world, every reader can predict their own future, and the outcome of the prediction will depend on their actions and choices. At the beginning of the story, Dohiko predicted his friend's future and made his friend a murderer. However, Dohiko did not give up hope. He decided to change his friend's future, but the process was very difficult and dangerous.
In addition to predicting the future, the future diary also involved some mysterious and supernatural elements, including time travel, parallel universes, and soul exchange. The story was full of suspense and horror elements, but it also explored topics such as human nature, morality, and faith.
In the world of the future diary, the manga and animation presented different story lines, including Dohiko's adventures, the process of changing his friend's future, and the struggle with the mysterious organization. The whole story was very fascinating, and it was a classic that was worth watching.