One possible interesting plot could be that Team 7 is trained by a new sensei who has a very different style from Kakashi. This new sensei focuses more on survival skills in extreme terrains. So, Naruto, Sasuke, and Sakura have to learn how to build shelters in deserts, jungles, and snowy mountains. They also learn to hunt for food and purify water in the wild. This new training makes them stronger both physically and mentally, and they develop new jutsu based on their experiences in these extreme conditions.
Well, if Naruto was trained by Danzo, he might be more ruthless at first. But joining Team 7 could soften him up. He'd probably bring some of Danzo's combat techniques and secrecy to the team. It could make for an interesting dynamic, with Naruto being a bit more of an enigma compared to his canon self.
A new character could be an old hermit who lives in a hidden cave in the mountains. This hermit has mastered a unique form of chakra control that allows him to manipulate the elements in ways not seen before. He takes an interest in Team 7 and decides to train them. He teaches Naruto how to combine his wind chakra with the earth beneath him to create powerful tornado - like attacks. For Sasuke, he shows how to infuse his fire chakra with lightning to make it more potent. And for Sakura, he helps her develop a new form of medical ninjutsu that can heal internal injuries more quickly.
If Naruto was trained by Danzo and joined Team 7 in a fanfic, his abilities would change significantly. Danzo's training would probably give him a more strategic mindset. He could be more proficient in using weapons and stealth. In Team 7, he'd learn to coordinate with Sasuke and Sakura. His chakra control might improve in different ways, and he could develop new jutsu that are a combination of what he learned from Danzo and what he discovers while on missions with Team 7.
Kosuke might be a character created specifically for this fanfic. He could be someone with a unique background, like perhaps he was once a disciple of a great ninja but then went on his own path. And now he sees potential in Naruto and decides to train him. He could have abilities that are different from the main characters in the original Naruto series, which is why he has something new to offer to Naruto in terms of training.
In this fanfic, Lilith could be an original character created by the author. She might be a powerful and mysterious figure with special abilities that make her suitable to train Naruto.
She could be someone with a special bloodline or ability. Maybe she has a unique form of chakra that gives her certain powers. In the context of training Naruto, her skills and knowledge are what make her important. She could be a mysterious figure who has been observing Naruto for a while and decides to take him under her wing to help him reach his full potential. For instance, she might have the ability to see the latent potential in others and wants to shape Naruto into a great ninja not just for his own sake, but also for the greater good of the ninja world.
It could lead to Naruto becoming even stronger and more skilled than in the original story. Jiraiya's training methods might unlock new powers for him.
It could be some of the younger ninjas from the village who look up to Naruto. Maybe a young genin who has a special ability with earth jutsu, and another who is really good at stealth but lacks confidence. Naruto would then help them grow.