Gaara is a very likely recipient. He was a Jinchuriki like Naruto and they have a strong bond. Naruto might send him letters to check up on him and continue their friendship.
It could also be a form of building alliances. By reaching out to the Jinchuriki through letters, Naruto is establishing a connection. This can be important in the Naruto universe where having allies is crucial for the safety of the villages and the world at large. He may be hoping to create a united front among the Jinchuriki against common enemies.
Boruto could be developed by showing his growth in responsibility. For example, in the fanfic, he could take on the task of teaching Himawari a new jutsu. This would not only show his skills but also his patience. Himawari, on the other hand, could be developed by showing her becoming more independent. Maybe she decides to go on a small mission on her own to prove herself to Boruto.
One possible scenario could be that the 5 - Tailed Jinchuriki has some sort of special power that draws both Itachi and Karin. Maybe Itachi is initially interested in the Jinchuriki for strategic reasons related to his Akatsuki duties, while Karin is intrigued by the unique chakra of the Jinchuriki. As the story unfolds, they all find themselves in a complex web of relationships and power struggles. Itachi might be conflicted between his loyalty to the Akatsuki and his growing feelings towards the Jinchuriki and Karin. Karin, on the other hand, could be using her own abilities to try and get closer to both of them for her own survival and perhaps a bit of romance.
The 'naruto jinchuriki of the world eater fanfiction' might center around the Jinchuriki's journey. Maybe they have to face challenges that come with being associated with a 'world eater'. This could involve battles against other powerful forces in the Naruto universe who either fear or want to use the power of the 'world eater' within the Jinchuriki. It could also delve into the Jinchuriki's relationships with other characters, like how Naruto's friends might react to this new and dangerous situation.
One possible fanfiction could focus on Hinata's journey through pregnancy. She might be filled with a mix of excitement and nervousness. Naruto, as her husband, would be very supportive, constantly bringing her comfort foods and making sure she's not overexerting herself. And as Himawari grows in Hinata's womb, Hinata could start daydreaming about what their daughter will be like, with her kind heart and strong will, just like her parents.
One great idea for a Boruto and Himawari fanfic is a story where they go on a journey outside the village. They might encounter new types of ninjas or strange creatures. Himawari could be the one to sense danger with her Byakugan first, and Boruto would be ready to fight. It would show their growth as ninjas and also their bond as siblings.
Often, other Naruto characters like Naruto Uzumaki or Kakashi Hatake might be included in the two - tails jinchuriki fanfiction. Their interactions with the two - tails jinchuriki can create new and exciting plotlines, whether it's them helping the jinchuriki control their power or going on adventures together.
Well, not having read the 'naruto jinchuriki of the world eater fanfiction', it's all speculation. The Jinchuriki is bound to be a main character. If it's set in the Naruto universe, Kakashi could also be in it. He might be in a position of trying to protect the Jinchuriki from those who would misuse the 'world eater' power. There could be a group of rogue ninjas who are after the Jinchuriki's power, and they could be major antagonists. And there may be a mysterious character who has a connection to the origin of the 'world eater' and has their own agenda regarding the Jinchuriki.