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.
One idea could be that the reborn character tries to prevent Obito's fall to the dark side. They could use their knowledge of the future to stop Madara from manipulating him. For example, they might intervene during the battle where Obito was thought to be dead and expose Madara's true intentions early on.
Another interesting point is the relationship dynamics. Obito, now as Sakura, has to navigate her relationships with characters like Kakashi. In some fanfictions, there are really intense and emotional scenes where Obito, in Sakura's form, tries to come to terms with his past actions towards Kakashi. Also, his relationship with Sasuke takes a new turn as he tries to understand Sakura's feelings for Sasuke from a different perspective.
One popular 'Obito reborn as Sakura fanfiction' might be 'A New Beginning'. In this fic, Obito's reincarnation as Sakura brings a whole new dynamic to the Naruto universe. It often explores how Obito's past experiences influence Sakura's actions and decisions in a very interesting way.
His personality would change in several ways. For one, he'd have to be more cautious. Obito was involved in a lot of secretive and dangerous operations. Naruto would have to adapt to this new level of secrecy. Also, he might become more brooding as he tries to understand Obito's darker motives in the original story. But ultimately, his strong belief in friendship and his never - give - up attitude would still be there, and he'd use them to make different choices than Obito did.
One interesting plot could be Naruto, now in Obito's body, trying to prevent the Uchiha massacre. He could use his knowledge from his past life to change the course of events and save his friends in the Uchiha clan. Another idea might be Naruto exploring Obito's relationship with Rin in a new way, bringing his own sense of loyalty and friendship to the dynamic.
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.
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.