One idea could be to create an OC who is a time - traveling medic. They could cross paths with the Doctor during the 'day of the doctor' and use their unique medical skills to help in a crisis. Maybe they have a device that can heal wounds in a different way than the Doctor's sonic screwdriver.
One idea could be that the OC is a long - lost relative of one of the main characters in 'knight and day'. They show up unexpectedly and have some special skills or knowledge that helps in the adventure. For example, they might be an expert in a certain type of martial art that is useful against the villains.
One idea could be an OC who is a brilliant scientist that discovers a new weakness in the alien technology just in time for the Independence Day battle. Another could be an OC who is a pilot from a small town and has to step up and fight the aliens, bringing a sense of hometown heroism to the story. Maybe an OC who is a diplomat trying to negotiate with other countries during the alien invasion to unite the Earth's defenses more effectively.
Perhaps an OC is a young archaeology student who idolizes Nathan Drake. They manage to get involved in one of his expeditions through sheer determination. Along the way, they learn from Drake and also teach him new things about modern archaeological research methods. It could be a story of growth and adventure for both characters.
Well, you could have an OC that is a skilled hacker who gets involved with the Phantom Thieves by accident. They might have a Persona that represents a famous code - breaker from history. Also, an OC who is a foreign exchange student from a country with a very different cultural background could bring in new elements to the fanfiction. Their Persona could be influenced by their home country's folklore. Maybe an OC who is a prodigy artist and uses their art skills to create powerful items in the Metaverse, with a Persona related to a great artist from the past.
You could have an OC that is a young witch who idolizes Bayonetta. She tries to copy Bayonetta's style and fighting techniques but often fails in a comical way at first. As the story progresses, she discovers her own unique way of being a witch. Or an OC who is a cursed object collector. This OC comes across Bayonetta when investigating a powerful cursed object and they end up working together to either destroy or control the object's power.
One idea could be an OC who is a spy sent to infiltrate Doflamingo's organization. This OC could have a hidden past that slowly gets revealed as they gain Doflamingo's trust. Another idea is an OC with a special power that Doflamingo wants to control or use for his own evil plans. For example, the OC might be able to manipulate time in a small area, which could be a great asset in battles or heists.
One idea could be to create an OC who is a new dancer in town. This OC could bring a different style of dancing to Footloose's world, like a fusion of modern and traditional dance. They could face challenges in getting the town to accept this new form of expression.
A great concept for superhero oc fanfiction is a hero who has the power of empathy. They can sense the emotions of others and use that to either calm down villains or boost the morale of their fellow superheroes. Also, you could write about a superhero oc from another dimension who comes to our world with powers that are completely alien to our understanding, like the ability to turn into a living energy form.
One idea could be to create a 2d oc who is a time - traveling detective in a steampunk world. They could solve mysteries that are related to the alteration of historical events.
One idea could be creating an OC that is a hybrid of two different Pokemon types. For example, a half - water, half - electric type with unique abilities. Another idea is to make an OC that has a special bond with a legendary Pokemon, perhaps they are the chosen one to help the legendary in a time of crisis. Also, you could have an OC from a different region with a completely new set of Pokemon not seen before in the main series.