In a 'naruto is a priest fanfiction', the plot could start with Naruto having a spiritual awakening. He then decides to become a priest. As a priest, he could be the mediator between the shinobi world and the afterlife. For example, there could be a situation where the dead souls of ninjas are restless and causing problems in the living world. Naruto, with his newfound priestly powers, has to find a way to pacify them. He may also have to deal with other religious or spiritual leaders in the Naruto universe who are skeptical or jealous of his new role.
One possible plot could be that Naruto, as a priest, is on a mission to cleanse the world of a dark curse that has been plaguing it. He would have to use his understanding of both the ninja world and the spiritual realm to succeed. He might face challenges from those who don't believe in his new role as a priest, and he'd have to prove himself. He could also be involved in helping people find inner peace and guiding them on a spiritual path, all while still having his ninja instincts and abilities.
Maybe Naruto could use his ninja skills in a more spiritual way as a priest. He could be protecting a sacred temple from evil forces that threaten the peace of the village.