One interesting OC concept could be a detective with a special ability like super hearing. They might be able to pick up on small sounds that help in solving cases, much like Conan's sharp observational skills but in a different way.
A third concept could be an OC who is a tech - genius. In the world of Detective Conan, technology plays a big role. An OC with advanced technological knowledge could develop new gadgets or use existing ones in unique ways to solve crimes, similar to how Conan uses his gadgets from Professor Agasa.
Another could be an OC who is a master of disguise. This OC could use their skills to infiltrate criminal organizations or get closer to the truth in a case. For example, they could disguise themselves as different suspects to observe their reactions more closely.
One interesting OC concept could be a high - flying daredevil OC who has a unique backstory of growing up in a circus and using those acrobatic skills in the WWE ring. Another could be an OC with a mysterious martial arts background, bringing in different fighting styles to WWE matches.
One idea could be creating an OC who is a master of disguise, like Conan, but with a unique backstory. Maybe they are from a different country and have their own reasons for getting involved in the detective work in Japan. Another idea is an OC that has a special gadget - something that hasn't been seen in the original series yet, like a device that can analyze poisons instantly. And a third idea could be an OC who is a childhood friend of Shinichi's that has some hidden talents related to solving mysteries that come to light after his transformation into Conan.
One interesting concept could be Conan traveling back in time to prevent the initial crime that led to his shrinking. He might be able to use his knowledge of the future to stop the Black Organization from ever getting to the point of drugging him. This would completely change the course of the story and perhaps even prevent the many tragedies that followed in the original plot.
One interesting OC concept could be a character with the power to manipulate time in the Mortal Kombat universe. This would add a whole new dynamic to the battles and storylines. For example, they could freeze time to dodge attacks or rewind time to correct a wrong move. Another could be an OC from a different realm entirely, with unique fighting styles and cultural backgrounds that contrast with the existing Mortal Kombat characters.
One interesting OC concept could be a vampire hunter who has a personal vendetta against the Lost Boys. They might be a skilled fighter with unique weapons.
Well, some OCs in Death Note fanfiction could be a psychic who can sense the presence of the Shinigami. This psychic might be drawn to the chaos that the Death Note is causing and try to use their powers to stop it. There could also be an OC who is a member of an underground organization that has been secretly studying the Death Note for years. They have their own motives, maybe to gain power or to prevent the wrong people from getting their hands on it. And an OC as a street - smart kid who stumbles upon the Death Note and has to make a choice between using it for personal gain or trying to destroy it, which would add a whole new perspective to the story.
Well, you could have an OC that is a childhood friend of Shinichi who has a photographic memory. This OC could recall small details from their past that end up being crucial in solving current cases. Or perhaps an OC who is an expert in a very specific field, like ancient languages, and Conan has to rely on this OC's knowledge when a case involves old inscriptions or manuscripts. Also, an OC who has a connection to the Black Organization, either as a former member trying to reform or someone unknowingly involved in their plans, could add a lot of drama to the fanfiction.
Well, an overpowered Naruto OC in gamer fanfiction might be one who has a unique chakra that can nullify any jutsu. Imagine in a battle against powerful foes like Pain or Madara, this OC just cancels out all their attacks with ease. Also, an OC with the power to communicate with all animals and gain their assistance would be quite overpowered. They could gather intel from birds, have wolves fight for them, etc.
One interesting OC concept could be a ninja from a small, forgotten village who has a unique chakra ability, like the power to manipulate sound waves for both offense and defense. This OC could come to Konoha and interact with the main characters, adding new storylines.
One interesting Detective Conan OC fanfic could be 'The New Detective in Beika'. It introduces a new original character who has unique deductive skills and gets involved in Conan's cases. Another great one is 'OC's Adventure in the Black Organization'. It gives a different perspective as the OC tries to infiltrate the Black Organization. And 'OC and Conan's Team - up' is also good, showing how an OC and Conan work together to solve mysteries.