It could also be a rogue Jedi who has fallen to the dark side. This character might feel jealous of Obi - Wan's ability to train the Star Killer and see it as an opportunity to gain power. So, they would try to undermine the training process and perhaps even try to take the Star Killer as their own apprentice.
Perhaps the fanfic could start with Obi - Wan finding the Star Killer in a difficult situation. He decides to take the Star Killer under his wing. During the training, they might face various challenges together, like attacks from Sith - related enemies. Obi - Wan would teach the Star Killer how to sense the Force, meditate, and use it for good. The Star Killer would grow in power and knowledge under Obi - Wan's tutelage.
Obviously, Naruto and Obi - Wan are the main characters. Naruto, the ninja from the Hidden Leaf Village, and Obi - Wan, the Jedi from the Star Wars universe. They are the focus as Obi - Wan is training Naruto.
The Akatsuki could still be the main antagonists. Even with Naruto's training by the Kyuubi, they would be after the tailed beasts. Their goals of collecting all the tailed beasts would put them in direct conflict with Naruto. And they have some really powerful members like Pain and Itachi.
Jon Snow could be one. He has a sense of honor and leadership, much like Obi - Wan. They could bond over their shared values and Jon could learn from Obi - Wan's wisdom. Another could be Daenerys Targaryen. She is on a quest for power and Obi - Wan might see her as someone who needs guidance to use her power responsibly.
It could be the other Hidden Villages. Since Naruto is becoming so powerful under Danzo's training, they might see him as a threat and try to stop him. Maybe they would send their best ninjas to take him down.
There could be new antagonists created specifically for this fanfic. Maybe some dark forces that were sealed away by Asura long ago are awakened. They would oppose Naruto because they see him as a threat to their resurrection or their evil plans.
It could be some rogue shinobi who are after Pakura's knowledge. Since she's training Naruto, they might see it as an opportunity to get to both of them and steal their techniques. Maybe they were once her enemies or just power - hungry individuals.
Obviously, Obi Wan is one of the main characters. There might also be other Jedi, perhaps his masters or his peers. And there could be villains or antagonists that he has to face in the story.
The main character is Obi - Wan Kenobi. And Anakin Skywalker also plays a crucial role as Obi - Wan's apprentice who later turns to the Dark Side. Yoda is another important character as he is a great Jedi Master and gives advice to Obi - Wan at times.
One possible plot could be that Obi - Wan is kidnapped by a new, unknown force in the galaxy. This force could be a secret organization that wants to use Obi - Wan as a bargaining chip against the Republic. Meanwhile, his friends and fellow Jedi, like Anakin, go on a mission to rescue him. Along the way, they discover the true motives of the kidnappers, which might be related to some ancient power or prophecy that Obi - Wan is unknowingly a part of.