Jane is likely a fan - created character. She could be an ordinary girl who somehow gets transported into the Naruto universe and starts writing a diary about her new life there.
Jiraiya is another person. Since Jiraiya trained Naruto and was like a father figure to him. Naruto could write about their travels together, the lessons Jiraiya taught him, and how much he misses Jiraiya after his death. He might also mention the pervy things Jiraiya did that always made him laugh.
Survival is also a big theme. Just like in the Future Diary anime where characters fight to survive in the deadly game, when combined with Naruto, it becomes about how the ninja from Naruto's world would handle such a life - or - death situation. They have to use their skills and wits not only against their enemies but also against the rules of the new, merged world.
One common theme is survival. Just like in the original Future Diary, the characters, often including Naruto, have to fight to stay alive in the dangerous situations presented by the diary. Another theme is power. Naruto already has his own set of powers in his universe, and when combined with the powers related to the Future Diary, it becomes a central focus on how he uses and controls these powers.
Well, it could be about Jane's experiences in the Naruto world. Maybe she's a new character who records her daily adventures, like her encounters with Naruto and his friends, and how she copes with the challenges of that world.
Maybe Naruto uses the diary to talk about his relationships. He could write about his friendship with Sasuke, how much he misses him when he's away, and his determination to bring him back. He might also write about his feelings for Sakura, like how he's trying to become someone she can rely on.
One great 'Naruto and Future Diary fanfiction' is 'The Ninja's Diary Quest'. It combines the ninja world of Naruto with the intense survival game concept from Future Diary in an interesting way. The characters are well - blended, and the plot keeps you on your toes.
The characters' interactions would be full of surprises. For instance, the more calculating characters from Future Diary might try to manipulate the Naruto characters for their own gain. But they'd quickly find out that Naruto and his friends are not so easily fooled. Naruto's friends like Sakura and Shikamaru would approach the Future Diary characters with different attitudes. Sakura might be a bit more cautious, while Shikamaru would be trying to figure out the best way to handle the situation. And the Future Diary characters would have to adapt to the different social and power dynamics of the Naruto universe.
A possible plot for this crossover fanfiction could be that the Future Diaries are actually some kind of ancient artifacts in the Naruto world that were lost long ago. Naruto discovers one while on a mission. The power of the diary starts to change the balance of power in the ninja world. Sasuke might be intrigued by Naruto's new power and at first be a bit jealous. But then they realize that they need to work together to stop a greater evil that is also interested in the power of the Future Diaries. The Future Diary characters would then come into play as either allies or enemies depending on their motives in this new world.
One great 'Naruto Future Diary' fanfiction is 'Naruto's New Path in the Future Diary World'. It has an interesting plot where Naruto gets thrown into the chaotic situation of the Future Diary and has to use his ninja skills and wits to survive. Another one could be 'The Bond between Naruto and the Future Diaries', which focuses on the relationships Naruto forms with the other diary holders.