One idea could be inserting yourself as a new mutant with a unique power that the X - Men initially suspect but then come to trust. For example, a power to manipulate time on a small scale, which could be used to save the team from a sudden ambush.
A great plot could be that you insert yourself as a mutant with the power to heal emotional wounds. In the world of X - Men Evolution, the mutants often face not just physical battles but also emotional traumas. Your character could help Jean Grey deal with the internal conflict of her powers, and also assist Cyclops in getting over his insecurities. This would bring a new dynamic to the team and also create interesting relationships within the X - Men universe.
One idea could be that you insert yourself as a skilled navigator who joins the Straw Hat crew and forms a special bond with Nami. You could help her create new and more accurate maps, and together face the challenges of navigating through uncharted waters. Another plot could involve you having a special power related to weather control, which complements Nami's own abilities with the Clima - Tact. You work together to protect the crew from powerful storms and enemies that use weather - based attacks.
You could insert yourself as a human knight. Picture this: you are part of the Stormwind army, and you get involved in the fight against the orcs. During a battle, you find a mysterious artifact that gives you special abilities. This leads you on a quest to find out more about the artifact's origin and how it can be used to save humanity from various threats like the Scourge or the demons.
Your self - insert could be a transfer student from another kingdom with a completely different fighting style. This would lead to interesting interactions with the main characters as they learn from each other. They might introduce new weapons or combat techniques that the others haven't seen before.
A possible plot is that the self - inserted character has to deal with the Omnitrix malfunctioning. This could lead to unexpected and sometimes comical transformations. They might transform into a really weak alien in the middle of a battle or into an alien that is completely inappropriate for the situation, like a tiny alien when they need to be strong. As they try to fix the Omnitrix, they learn more about its inner workings.
The OC could be a mutant from a different country who comes to the X - Men school. Pietro is immediately intrigued by her different culture and way of using her powers. They start to exchange stories about their mutant experiences, and a relationship forms based on mutual understanding and respect for their differences.
One plot idea could be that the OC is a new mutant at the school and Kurt is assigned to show them around. They start off as friends but gradually develop deeper feelings as they face challenges together, like dealing with a bully mutant. Another could be the OC has a special power that Kurt needs to help control, and in the process, they bond over their shared experiences of being different.
One idea could be an OC with a unique power that attracts the attention of multiple X - Men characters, leading to a harem - like situation. For example, an OC who can manipulate time on a small scale. This power could be both useful and dangerous, and different X - Men might have different reactions to it, some being intrigued and others being cautious.
A plot idea could be that Bobby and Jubilee get trapped in a time - loop. Each time they relive the day, they notice different things about each other and their powers. At first, they're frustrated, but as they work together to break the loop, they develop a deeper understanding of one another.
One idea could be that Hela, as the self - inserted character, tries to reform the Avengers from within. She could use her unique powers and knowledge of Asgardian lore to help them face a new, powerful enemy. Maybe she starts off as a suspicious figure but gradually gains their trust through her heroic deeds.
A good plot for Highschool DxD self - insert fanfiction might be that the self - insert character is actually a reincarnation of an ancient and powerful being. They start off not knowing this, but as the story progresses, they gradually unlock their past memories and powers. This could lead to them having to make choices between their new life in the Highschool DxD world and their old responsibilities from their past life.