The main characters are Naruto and Kushina. Given that it's about Kushina inside the seal within Naruto, their relationship and interactions would be at the heart of the story. It's possible that other characters from the Naruto universe could play supporting roles. For example, the Nine - Tails might also be important as it is also associated with the seal. But overall, Naruto and Kushina are the key figures in this fanfiction.
I'm not entirely sure as I haven't read this specific fanfiction. But it might involve Kushina's presence inside the seal in Naruto's body and some sort of unique interaction or adventure that takes place within that sealed space. Maybe she imparts some special knowledge or power to Naruto.
Well, Naruto and Kushina are central, but antagonists could also be important characters. Maybe there are some rogue ninja who oppose Naruto's new - found dominance and target Kushina to get to him. This would set up a conflict where Naruto has to use his dominance not just to show off but to actually protect Kushina from real threats. So, the main characters would be Naruto, Kushina, and potentially these opposing forces.
The main character is Naruto. However, there could be new characters created specifically for this fanfiction. For example, an ancient being that has been living inside the Shinju for ages. And of course, some of Naruto's mentors or enemies from the original series could also make an appearance, depending on the direction the fanfiction writer wants to take. If it's about Naruto facing a new threat inside the Shinju, an old enemy could be resurrected in a different form inside the Shinju's realm.
There might also be other characters involved. For example, Minato might make an appearance in flashbacks. Since he was Kushina's husband and Naruto's father, his presence could be important in terms of the backstory. Also, characters from the Hidden Leaf Village might be mentioned or even try to find Naruto and Kushina, like Iruka Sensei who has a special bond with Naruto.
Obviously, Naruto would be the main character. Then there would be Minako and Kushina, his mothers. They would play important roles in shaping Naruto's life. There might also be characters from Minako's family, like her relatives or clan members, who could be introduced to the story.
Iruka could be one of the characters. He has always been important to Naruto, and he might try to help Naruto or at least be concerned about his exile. Kakashi could also appear. He has a connection to Naruto and might be conflicted about the situation. And then there are Naruto's friends like Sasuke and Sakura. Sasuke might understand Naruto's feeling of being an outcast more than others, and Sakura could be torn between her loyalty to the village and her friendship with Naruto.
The two main characters are Naruto and Kushina. Naruto, with his godlike powers, is going to be a major driving force in the story. He will use his powers in relation to Kushina, whether it's to protect her, help her, or just be with her. Kushina, on the other hand, will be the character that Naruto's actions are often directed towards. Their personalities and how they mesh together because of Naruto's special status will be what makes up the heart of this fanfiction.
Most likely Naruto himself would be one of the main characters. He's the titular character of Naruto. And probably some of his close friends like Sasuke and Sakura. From High School of the Dead, it could be Takashi Komuro.
Naruto himself is very likely to be a focus. His complex personality and strong emotions make him a prime candidate. Also, Sasuke, with his brooding nature and his past traumas, would be another. His internal journey of revenge and later redemption can be explored in an 'inside out' way.
Most likely Naruto will be the central character. Alongside him, we can expect to see his usual companions. Sakura could be there, perhaps providing some medical support or getting involved in a beach - related mystery. Sasuke might be there too, either as a friend or with some ulterior motives. And Kakashi could be there to guide the young ninjas, especially if there are any dangerous situations or training opportunities on the beach.