One plot idea could be that the male OC is a new student at True Cross Academy. He's a bit of an outcast because of his mysterious past. As he tries to fit in, he discovers a hidden plot within the academy that involves demons. Another idea is that he has a special power that the exorcist order wants to use for their own purposes, but he has to decide whether to cooperate or not. A third plot could be that he is on a quest to find a lost artifact that has the power to either destroy all demons or give them ultimate power, and he has to face many challenges along the way.
A good plot could be that the male OC is actually a half - demon, and he's trying to keep it a secret while living among the exorcists. He constantly struggles with his demonic side, especially when faced with strong emotions. This could lead to some internal conflicts and interesting storylines. Or, he could be a time - traveler from the future, where the world has been taken over by demons. He comes back to the present to try and change the future, but has to convince the current exorcists to believe him. Also, he might get involved in a love triangle with two existing characters, which adds a romantic and dramatic aspect to the fanfiction.
Here are some plot ideas. The male OC could be a prodigy exorcist, but he has a dark secret that could ruin his reputation. Maybe he made a deal with a demon in the past to gain his powers. As he rises in the ranks of the exorcist community, this secret starts to surface. Another plot is that he is sent on a mission to a foreign land where the exorcist ways are different. He has to learn their methods and work with local exorcists to defeat a powerful demon that is terrorizing the area. And, he could be framed for a crime he didn't commit within the exorcist order, and has to clear his name while also dealing with the real culprit who is still causing chaos.
Well, for Blue Exorcist OC fanfiction, you could have a plot where your OC is a hybrid of a human and a demon. This causes a lot of internal conflict as they struggle with their identity and are feared by both sides. They try to find a place where they can belong. Another plot idea is that your OC is a master of a new form of exorcism that is not recognized by the True Cross Order. They have to fight to get their method accepted while also using it to combat a new wave of powerful demons. And then there's the idea of your OC getting caught in the middle of a power struggle between different factions within the exorcist world, having to choose a side while trying to stay true to their own beliefs.
One idea could be an OC tamer who has the ability to communicate with rare and powerful demons. For example, they might be able to understand the language of ancient demons that others can't. This would give them an edge in battles and in understanding the demon world better.
For an Inuyasha male OC fanfiction plot, consider this. The male OC is an artist who can paint things that come to life. He gets caught up in the chaos around the Shikon Jewel when one of his paintings accidentally becomes a powerful demon. Now he has to work with Inuyasha and the others to defeat it. Or he could be a demon slayer who has a personal vendetta against a particular type of demon that is also involved in the Shikon Jewel saga. His presence disrupts the group's dynamics at first, but they soon realize they need his skills. Another idea is that he's a messenger from another dimension who brings news of a greater threat that will affect not only the Inuyasha world but also other dimensions.
One plot idea could be that the cat OC is a reincarnation of an ancient exorcist. It slowly starts to remember its past life as it encounters different demons and exorcists. This could lead to a journey of self - discovery and also help the main characters in their fight against stronger demons. Another idea is that the cat OC has a special bond with a powerful demon, but it has to keep this a secret from the exorcists. This creates a lot of internal conflict and also the potential for some tense moments when the secret is almost revealed.
A male OC could be a Muggle - born who discovers he has a special power that the wizarding world has never seen before. He could be hunted by dark forces who want to use his power for evil, and he has to rely on his new friends at Hogwarts to protect him. Another idea is that the male OC is a transfer student from a foreign wizarding school. He brings with him different magical techniques and cultural beliefs, which causes a stir at Hogwarts as students and teachers alike are both intrigued and a bit skeptical.
Here's a plot idea. The male OC is an alchemist who has a special connection to the Truth. He starts having visions of a coming catastrophe that is related to the misuse of alchemy. He has to convince the other alchemists, including Edward and Alphonse, that this is real and they need to work together to prevent it. This could involve him traveling across the country, facing various challenges and enemies along the way. Another plot could be that he's a foreign alchemist who comes to Amestris to study their alchemy. But he soon realizes that there are dark secrets within the Amestrian alchemical community that he must expose.
One plot idea could be that your OC discovers a hidden power within themselves that is connected to an ancient prophecy. They then have to figure out how to control this power while also dealing with the other exorcists who are either suspicious or jealous of them. Another idea is that a powerful demon has a special interest in your OC and is constantly trying to either turn them to the dark side or use them for some evil purpose. Your OC has to resist and find a way to defeat this demon.
One plot idea could be that the male OC is a detective hired to investigate strange disappearances in the Black Butler world. He starts to suspect that there's a supernatural force at work and teams up with the main characters to solve the mystery. Another idea is that he's a nobleman's son who has a secret identity as a vigilante, fighting against the corrupt nobles. He might cross paths with Ciel and Sebastian when they're on a mission related to the same nobles.
A plot could involve the male OC being related to one of the scientists who worked at the lab. He comes to Hawkins to find out what really happened to his relative. Along the way, he teams up with the kids and they uncover a conspiracy that goes deeper than they thought. Or perhaps the male OC is an artist and he starts having visions of the Upside Down through his art, which leads him on a journey to figure out what they mean.
Well, here's a plot idea. The male OC has a special connection to a magical artifact that is coveted by an evil force. He has to protect it while also trying to figure out why he has this connection. Also, he could be in a love triangle with two other characters in the guild, which adds a lot of drama to the story. Another idea is that he's the key to unlocking a hidden power within the Fairytail guild, but he doesn't know it at first and has to go through a series of trials to discover his true potential.