Maybe an OC who is a long - lost relative of one of the main characters. This OC could come to the neighborhood with a secret that shakes up the relationships among the characters, like a hidden inheritance or a family feud from the past. For example, if they are related to Cesar, it could create tension between him and his gang - affiliated family as the OC has different values.
An OC could be a foreign exchange student who moves into the block. They don't understand the local culture and the complex relationships at first. But as they interact with the main characters, they start to learn and also introduce their own culture, which leads to some really interesting cultural exchanges and new friendships.
One idea could be an OC who is a new student at the school in 'On My Block'. They could have a unique talent like being an amazing street artist and use it to bring the community together for a local art project.
One idea could be exploring the backstories of the characters more deeply. For example, delving into how Monse became so strong - willed. Another could be creating a time - skip fanfiction where the characters are in college and how their relationships have changed. Or you could write a fanfiction where a new character arrives in the neighborhood and shakes up the dynamics among the main characters.
One idea could be an OC with a unique quirk that doesn't seem powerful at first but has a hidden potential. For example, an OC who can manipulate shadows in a very limited way, but discovers they can use it to travel between dimensions in the shadows. Another could be an OC who is a foreign exchange student with a quirk that is considered abnormal in the My Hero Academia world, like a quirk that allows them to communicate with plants and use them as allies in battle. Or an OC who has a quirk that lets them see the future but only in their dreams, and they have to figure out how to use this information to help their classmates and heroes.
One idea could be a female OC who has a unique quirk related to sound manipulation. She could use it to both heal and attack. For example, she might be able to use certain frequencies to soothe injured heroes or use ultrasonic waves as a weapon against villains. Another plot could involve a female OC from a foreign country coming to study at U.A. High School. She has to deal with cultural differences while also trying to fit in with the other students and prove herself as a hero. A third idea is a female OC who discovers an ancient quirk that has been lost for generations and has to learn how to control it while also facing those who want to steal her new - found power.
A cool plot for a male oc fanfiction could be an oc who is from a family of villains but wants to be a hero. He has to constantly fight against the stigma and suspicion from his classmates and teachers. He might have a quirk that is seen as villainous, like the power to create illusions that can cause fear, but he uses it in positive ways, like creating distractions during rescue missions. Also, an oc with a quirk that lets him transform into different elements could be interesting. He could struggle with controlling his powers at first and accidentally turn into water during a classroom session.
One idea could be a female OC who is a talented artist in Equestria but is too shy to show her work. She then meets one of the main ponies like Twilight Sparkle who encourages her to share her art with the world. Another could be a female OC from a different land who comes to Equestria to learn about friendship and has to overcome cultural differences.
One idea could be an OC who is a new vampire in town and befriends the babysitter vampire. They could team up to protect the neighborhood from a new threat, like a group of werewolves.
The OC could have a quirk that gives them the ability to see all possible futures. This would make their decision - making in battles very crucial. They might struggle with the weight of this knowledge at first, but as they learn to trust their instincts and use their quirk effectively, they become an invaluable asset to their hero team. They could also use this quirk to prevent major disasters in the My Hero Academia world.
Perhaps the OC has a hidden past related to a villain organization, and the harem members are initially suspicious but as they get to know the OC better, they realize there's more to the story. This could create a lot of drama and conflict as the OC tries to prove their loyalty while also dealing with their growing feelings for the harem members.
Another plot could revolve around an OC who is a Spartan trainee that doesn't quite fit the mold. They have a different way of thinking and approaching combat. In Halo 4, they end up being the key to solving a mystery related to the Prometheans. Maybe they find a way to communicate with the Prometheans and convince some of them to stop fighting the humans.
One idea could be an Otsutsuki OC who comes to Earth not for conquest but to study the unique life forms here. They could befriend some of the local ninjas and learn about the concept of friendship, which is alien to the Otsutsuki. This would lead to a series of adventures where they have to protect their new friends from other more hostile Otsutsuki members.