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.
Minato might also be a prominent character. As their teacher, he can influence the way Obito and Kakashi interact. In some fan fictions, he could be the one to help them resolve their differences or provide some crucial information about their past that changes their current situation.
The main character is Obito without a doubt. The other main character in the 'obito love story' could be a character from a different clan. Their different backgrounds would add more depth to the story. For instance, if Obito is from the Uchiha clan and the love interest is from the Hyuga clan, their relationship would be full of cultural and clan - related tensions, making their love story all the more interesting.
One potential antagonist could be the Hidden Mist ninjas. They are known for their ruthless tactics, and they might target Rin for some strategic reason. Maybe they think she has valuable information about Konoha's defenses.
Kakashi could also be included. He has a history with Obito, and his relationship with Itachi was also complex. His skills and his role as a mentor - like figure can bring a different dynamic to the story. For example, he could be the one who suspects something strange is going on between Itachi and Obito and tries to figure out their motives.
Well, it's hard to say who the 'best' is as it depends on personal taste. But some popular authors might be those who really capture the essence of the characters. For example, there are authors who are great at writing Kakashi's calm and collected nature while also showing his inner turmoil. They can make his relationship with Obito feel very real and complex.
In a Naruto - Dragon Ball Z crossover, Goku could be a great character to cross with Obito. Goku's pure - hearted nature and his super - strong combat abilities would contrast and interact interestingly with Obito's more complex and often - conflicted character.