The plot could start with Naruto being the only one who can see a strange kind of demon that the regular exorcists can't detect. This makes him a valuable asset. So, he teams up with the exorcists. As he works with them, he discovers that his chakra has some similarities to the exorcist powers. He then starts to train with them to enhance his new - found abilities. During this process, he faces challenges from both the ninja world and the exorcist world, as some people are skeptical or even hostile towards him for being different. But through his determination and the friends he makes, he overcomes these difficulties and becomes a great exorcist - ninja hybrid.
One possible plot could be that Naruto discovers he has exorcist powers in addition to his ninja abilities. He then has to learn how to control and use these new powers while still dealing with the threats in his ninja world.
Maybe Naruto gets transported to the world of exorcists. There, he meets the exorcist characters and has to prove himself. He could use his ninja training to fight the demons in the exorcist world in a unique way. And along the way, he might make new friends and enemies, and his view of the world could change as he experiences the exorcist way of life.
One possible plot could be Naruto being summoned to the DxD world by some sort of magical accident. He could then use his ninja skills, like his shadow clone jutsu, in unique ways to combat the devils and exorcise evil spirits. For example, his clones could be used to surround and confuse enemies during an exorcism battle.
The plot could involve Naruto using his ninja skills in the world of exorcism. He might use his shadow clone jutsu to outnumber demons. For example, he could send clones to different areas to search for and fight demons while he focuses on the stronger ones. His Rasengan could be modified to have an exorcising effect, perhaps by infusing it with spiritual energy.
It could be about Naruto somehow ending up in the world of Blue Exorcist and taking on the role or having the abilities of Rin. Maybe he has to fight demons in the Blue Exorcist style while still having his Naruto - like skills.
One likely main antagonist could be a powerful demon lord who is trying to break through the barriers between the spirit world and the human world. This demon lord would be a major threat to Naruto and his harem, and they would have to use all their combined skills to stop it.
One plot idea could be that Naruto, with his immortality, somehow gets transported to the world of Blue Exorcist. He teams up with Rin and the others to fight a new kind of demon that is threatening both their worlds. His ninja skills combined with the exorcist powers would make for an exciting adventure.
A third plot idea is that some of the characters from Blue Exorcist end up in the Naruto universe. Rin and his friends could be intrigued by the concept of ninjas and chakra. They might learn some ninja techniques and in turn, teach the ninja about exorcism. This could lead to a new generation of ninja - exorcists in the Naruto world. They could also help the ninja deal with a dark force that has some similarities to demons from their own world.
One possible plot could be that Rin's demonic powers go haywire during a difficult exorcism. As a result, his body starts to regress into a baby form. His friends at True Cross Academy would be super confused. Yukio might initially think it's some kind of new demonic curse. They would then have to figure out how to reverse the process while also protecting baby Rin from other demons who might see him as an easy target.
Well, it could be a story where Rin and Shiemi are on a mission together. As they face a powerful demon, Shiemi gets injured. Rin, worried sick, nurses her back to health. In a moment of relief and new - found closeness after the ordeal, they share a kiss. It's a sign of their growing bond and the start of a deeper relationship.
Power-ups are a common theme. Since Naruto already has his ninja powers and then enters the DxD world with its own set of powers like Sacred Gears, a lot of fanfics focus on how he combines or enhances these powers. For example, he might learn to use his chakra in new ways because of the DxD environment.
The plot might involve Rin using his skills as an exorcist to deal with the challenges of being a tamer. He could encounter various types of creatures that need taming. Since he has the power of Satan within him, it could add an interesting twist. He might struggle to control his inner demon while trying to tame other beings, and this internal conflict could drive the story forward.