Perhaps the oc with the evil quirk is recruited by a villain group. They initially resist but the group somehow convinces them that the world is against them because of their quirk. So they start to use their evil quirk for the villains' purposes, like stealing or causing chaos. However, as they do more bad things, they start to have second thoughts and might try to break away from the villains.
One possible plotline could be that the oc with the evil quirk tries to hide it from others at first. They might be afraid of being ostracized. For example, they could pretend to have a normal quirk in public but struggle internally with the dark impulses their evil quirk brings. Another plotline could involve the oc being forced to use their evil quirk for self - defense in a dangerous situation and then having to deal with the consequences of others seeing what they can really do. Maybe they get hunted down by heroes who misinterpret their actions as villainous.
In some stories, the oc's evil quirk could be something that is misunderstood. It might look evil on the surface, like being able to control shadows which is often associated with darkness and evil. But in reality, they could use it for good. For instance, they could use the shadow - controlling quirk to save people from falling debris by creating a shadow - shield. But most people don't trust them because of the appearance of their quirk.
One way is through self - sacrifice. If the character uses their evil quirk to save a lot of people at great personal cost, it could be a step towards redemption. For example, if their quirk is something like mind - control and they use it to stop a powerful villain who is about to destroy a city, but in the process they lose their own ability to use the quirk. Another way is by showing remorse and actively trying to make up for their past actions. They could start doing volunteer work in the community, using whatever skills they have (even if related to their quirk in a non - evil way) to help others.
Well, perhaps the story could be about the daughter discovering her own unique abilities that are different from Kakashi's. This could lead to some interesting father - daughter bonding moments as he tries to help her develop those powers. Also, there could be a plotline where the daughter gets involved in a mission that is related to Kakashi's past, and they have to work together to solve it.
One interesting plotline could be Izuku using his voice quirk to communicate with animals. Since many animals respond to different frequencies and tones, his voice quirk might allow him to understand and direct them. For example, he could use it to get a flock of birds to create distractions during a villain attack. Another plotline might involve Izuku using his voice quirk to soothe people in distress. His voice could have a calming effect, which would be useful in rescue situations or when dealing with panicked civilians. And a third plotline could be Izuku having to train his voice quirk in secret because it's considered too dangerous or unpredictable, and he has to find unique ways to control and develop it without getting caught by the wrong people.
One interesting plotline could be Izuku using his Pokemon - like quirk to battle villains in a unique way. For example, he might summon Pokemon - inspired creatures with different powers to counter various villain attacks.
There could be a story where the OC's dark quirk is a secret at first. They are living a normal life until certain events start to trigger the quirk. The fanfiction might explore how they keep this secret from their friends and family. As the story progresses, they might be forced to reveal it when facing a powerful enemy that only their dark quirk can defeat. This could lead to a lot of drama, with their loved ones having to come to terms with this new side of the OC.
A third plotline could be Izuku being targeted by villains who are interested in his black lightning quirk. They might see it as a powerful tool or a key to some greater scheme. This would put Izuku in a dangerous situation and force him to rely on his friends and his own growing skills to protect himself and the ones he loves. His friends might also have to step up and help him develop new strategies to combat these villains who are specifically after his quirk.
One possible plotline could be that Ash is betrayed by his friends. This heartbreak and sense of abandonment turns him evil. He then starts using his Pokémon in cruel ways to seek revenge on those who wronged him.
One possible plotline could be Naruto getting corrupted by an ancient and powerful evil entity. This entity could influence him to turn against Konoha and start his reign of terror. He might use his knowledge of the village's secrets to his advantage in causing destruction.
One possible plotline could be that Naruto is influenced by some dark force and turns 'evil'. Kushina, having come back to life somehow, tries to understand what has happened to her son. She then embarks on a journey to find a way to reverse the effects, leading to a series of adventures where they interact in different ways, like Kushina trying to jog Naruto's memories of their family bond.
One possible plotline could be that Harry discovers a dark secret about his family and feels betrayed by the wizarding world. This could lead him to side with the dark forces. Another could be that he is influenced by a powerful dark wizard who manipulates his mind. Maybe he becomes envious of the power others hold and decides to take it by any means, turning evil in the process.