Well, Naruto's friends and comrades from his past adventures are likely to be in it. But also, there could be some spiritual or mythical characters related to the concept of the golden fox. For example, there might be an old sage who knows the secrets of the golden fox and can guide Naruto on how to use its power properly. There could also be other villages' representatives who come to Konoha to see this 'Naruto with the golden fox' phenomenon and see if it poses a threat or an opportunity for their own villages.
Well, it could be about Naruto coming back to Konoha with some new powers related to the golden fox. Maybe he uses these powers to protect the village from a new threat.
Obviously Naruto is one of the main characters as it's related to him. And the Nine - Tailed Fox would also be a central figure considering the title. Also, characters like Sasuke and Sakura are likely to be important as they are Naruto's friends and comrades in the original Naruto series and would surely be involved in the events of the fanfiction.
There could be new ninja from other hidden villages that are introduced when Naruto returns. Maybe a powerful young ninja who wants to test his skills against Naruto. Or perhaps a mysterious sage - like figure who has some connection to Naruto's new power.
There could be a powerful mentor figure that Naruto met during his time away. This person might have taught him the secrets to his newfound strength.
In this fanfiction, Naruto is the key figure. However, characters like Shikamaru, who is known for his intelligence, might also be involved. He could be helping to plan Naruto's welcome or dealing with any potential issues that Naruto's return might bring. Also, Hinata, given her relationship with Naruto, would surely be part of the story. And the elders of the village may also play a role, as they often have a say in important matters regarding the village and its shinobi.
Aside from Naruto and his immediate family, characters like Kakashi could also be important in this fanfiction. He was Naruto's mentor, and he would surely be there to welcome them back. And Sasuke might also play a role, as he is Naruto's friend and has a connection to the village too.
It's possible that the child is an orphan Naruto found. Naruto, having known the pain of being alone as a child, decides to take the orphan under his wing. He brings the child back to Konoha to give it a home and a family within the village.
It could be a rogue ninja who has been secretly building power while Naruto was away. This rogue ninja might have a vendetta against Konoha and sees Naruto's return as a challenge to his plans. So he directly confronts Naruto to prove his own strength.
The devils that oppose Rias' group could be the antagonists. They might see Naruto as an unknown threat and try to eliminate him. Also, there could be some dark magic users who don't want Naruto interfering in their plans in Rias' world.
Well, in the 'naruto trains and returns to konoha fanfic', Naruto is the central figure. For his training, he could meet some new characters who are experts in certain ninja arts. But in Konoha, all his old comrades will be there. Shikamaru, who is known for his intelligence, might be involved in planning something related to Naruto's return. Ino could be there too, perhaps using her mind - related jutsus to help in some way. And of course, the old sages or elders of Konoha would also be present to assess Naruto's growth and the impact of his return on the village.