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 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.
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.
An interesting plot could involve an OC who is initially thought to be quirkless but discovers a latent quirk later on. This OC could then struggle to catch up with the others in terms of training and development. Or, an OC with a shapeshifting quirk could be used in a plot where they have to infiltrate a villain's lair by taking on the form of one of the villains' minions. They would have to be careful not to be discovered and also gather intelligence along the way.
Well, he could be an OC with a healing quirk. In the fanfiction, he starts helping out injured students during training sessions. This catches the attention of several female characters. Some might see him as a valuable asset to their future hero teams, while others develop a more personal attraction. The harem could then be formed as these girls start competing for his attention in a friendly way, like trying to bring him the best lunches or inviting him to exclusive study sessions.
One plot idea could be that the Saiyan OC is mistaken for a new type of villain at first. As they try to prove they're not a threat, they start to make friends and learn about heroism. Another idea is that they discover a connection between Saiyan powers and some of the hidden secrets in the MHA world. Maybe there's an ancient power source that only a Saiyan can unlock.
A great plot could involve the ruthless OC being a double agent. They pretend to be a hero but are actually working for a secret villain group. As they interact with the heroes, they start to have doubts about their loyalty to the villains. Maybe they fall in love with a hero, which further complicates things. Another plot is that the OC has a vendetta against a particular hero or villain family. They use their ruthless tactics to systematically take down members of that family one by one. Also, the OC could be part of an experiment that gives them super - ruthlessness, and they have to deal with the consequences of this new - found trait.
An interesting concept would be an OC who has a quirk that is based on art. For example, they can bring paintings to life. This OC could be a part of an art school within the My Hero Academia universe and use their quirk to fight villains who are attacking art galleries or museums. They would also have to train their quirk to be more combat - effective.
One plot idea could be a villain who is secretly a double agent, working for the heroes all along. They infiltrate the villain group and gather information. Another idea is a hero who loses their quirk and has to rely on their wits and combat skills alone, like Batman in the DC universe. And a villain - hero team - up to face a greater threat that neither can handle alone.
An interesting plot could involve an anti - hero who has a hidden agenda that is not entirely evil but also not in line with the traditional hero goals. Maybe they are trying to expose a corrupt part of the hero society from within. They could form alliances with some villains who also have a vendetta against the corrupt elements. This would create a complex web of relationships and moral dilemmas.