One possible interesting plot could be Obito revealing his true identity to the Akatsuki members. It would create a huge shock and change the dynamics within the group.
Naruto could be one of his allies. Naruto has this knack for seeing the good in people and would probably be willing to give Obito a chance to redeem himself. Also, Sakura, with her skills as a medic - ninja, could be an ally. She might help heal Obito if he was injured during the war and see the potential in him to be a force for good.
There could also be interactions with the new generation of ninjas. They might view Obito as a sort of legend or a cautionary tale. Their fresh perspectives could either inspire Obito to change further or make him feel even more out of place in this new post - war ninja world.
Well, the reborn character could explore Obito's Sharingan powers in new ways. Instead of using them mainly for combat like Obito did in the original story, they could focus on using the Sharingan to understand the emotions of others. For example, they could use it to detect lies and hidden motives, which would be a unique twist on the power.
Besides Obito, Sasuke could be a main character in this fanfiction. Sasuke, with his own journey of redemption and his understanding of power and the ninja world, could have an interesting dynamic with the reincarnated Obito. Also, Sakura might play a role. She could be the one who tries to heal the reincarnated Obito, both physically if he is injured during his new adventures and emotionally from the traumas of his past life.
Often, Obito is attracted to Kushina's strength and kindness. He might try to impress her with his own abilities. Their interactions could involve Obito being a bit clumsy in his attempts at first. Kushina, on the other hand, might find his eagerness endearing and start to open up to him more. They could share stories about their pasts, their dreams, which deepens their bond.
One possible fanfiction could be about Naruto and Obito teaming up to face a new, powerful enemy. They could combine their unique skills, like Naruto's Rasengan and Obito's Kamui. Their relationship could start off rocky due to their past differences but gradually turn into a strong bond as they fight side by side.