One idea could be an OC who discovers their psychokinesis quirk gradually. They start with small things like moving a pencil, then as they train, they can lift heavier objects. This can lead to an interesting story arc of self - discovery.
Well, you could have an MHA OC who is a villain - turned - hero. Their backstory could involve being mistreated and turning to villainy, but then being inspired by the heroes to change their ways. Maybe they have a quirk that involves shadow manipulation, which they used for evil before but now use for good. Or an OC that is a tech - genius and creates their own high - tech hero gear, much like Mei Hatsume but with their own unique style. Also, an OC with a healing quirk could be interesting, especially if they have to deal with the moral dilemma of whether to heal villains or not.
The new quirk of Deku is quite exciting and adds a new dimension to his powers. But I don't want to spoil it for you. You should read the manga to find out!
One idea could be an OC with a sound quirk who can manipulate sound waves to create illusions. For example, in a battle, they make the enemy think there are multiple allies when it's just sound - based images. Another could be an OC that uses their sound quirk to communicate with animals, as different frequencies might be understood by them. A third plot idea is an OC with a sound quirk in a music - based society where their quirk gives them an edge in creating the most beautiful and powerful music, but they face jealousy from others who don't have such a useful quirk.
One idea could be to make the character with the lightning quirk have a fear of water. This would add an interesting dynamic as lightning and water don't mix well. They could struggle to control their quirk when near water, and it could be a source of internal conflict for them.
Perhaps an ancient artifact in the MHA world has the power of the Naruto toads sealed within it. A villain discovers it first but a young hero - in - training manages to steal it away. Once in their possession, they unlock the toad quirk. They would then need to train hard to master it, just like Naruto did. They could call on the toads for help in battles, use their strong physical attacks and even learn some of the toad - related ninjutsu, adapting it to fit the rules and physics of the MHA world.
They would be very powerful. Just like Naruto can summon giant toads, this character could summon toads in the MHA world. They could use the toads as mounts or have them fight alongside. For example, they could have a toad use its tongue to grab villains and hold them in place.
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.
The OC could start as a shy and withdrawn character, afraid of their psychokinesis quirk. But as the story progresses, they gain confidence. For instance, at first, they might accidentally break things with their quirk and be scared, but later they learn to control it and become more self - assured.
There's 'A New Hope for UA' which is also a very good MHA OC fanfiction. In this, the OC has a quirk that is initially seen as weak but they manage to use it in innovative ways. The fanfiction does a great job of integrating the OC into the existing MHA universe, with lots of references to the original series.