Well, your OC could be an exchange student from another country with a very different quirk culture. They bring new ideas and techniques to the My Hero Academia world. But they also face discrimination or misunderstanding from some of the local students. This could lead to a story about cultural exchange and acceptance. Another plot could be that your OC's quirk has a side - effect that they only discover later. This side - effect could be either a great power or a great danger. And they have to figure out how to deal with it while still being a hero. Or perhaps your OC discovers an ancient prophecy related to quirks and they are the key figure in it. This would involve them going on a quest to fulfill the prophecy and facing many challenges along the way.
One plot idea could be your OC starting at a new hero school. They have to deal with fitting in, making friends, and facing rivals. Another is that your OC discovers a new type of quirk that is being hunted by villains. They then have to protect this knowledge while also learning to control their own quirk better. Or, your OC could be wrongly accused of a crime committed by a villain with a similar quirk. They have to clear their name while also dealing with the public's distrust.
Chapter 927, "Jiang Li: Deceased, Do Not Disturb", is the clearest early answer because it turns Deceased's situation into a concrete plot event.
Chapter 914, "A Married Daughter is Like Spilled Water!", is the clearest early answer because it turns Like Spilled Water's situation into a concrete plot event. Early on, Jiang Li let out a cold laugh.. By the end, This revelation got the fans even more excited..
If you want the clearest chapter reference, go to Chapter 38. Early on, Jiang Li had also observed the girl who had just entered.; later, the chapter leans on Before arriving, she had briefly reviewed the profiles of the other three....
Chapter 929, "Award Ceremony", is the clearest early answer because the buildup finally cashes out in a real clash. A useful checkpoint is the way the scene starts with The Golden Statue Award is considered the most prestigious award in...
The best chapter pointer here is Chapter 51, "The Great Lodging Competition". It opens with Oh, okay." After uttering two syllables indifferently, Jiang Li bent down... and closes on If I opened a bar here, wouldn't I become a savior?" Jiang Yan was....
The best chapter pointer here is Chapter 34, "Official Recording!". It opens with Seeing that the public sentiment wasn't quite right, Su Yinwan felt... and closes on Now that Lili is misunderstood, they start to kick us while we're down."....
A practical answer is Chapter 22, because it turns the idea into a concrete scene. The chapter opens with Hearing this, Su Yinwan looked at Shang Shaojing with a face full of..., adds pressure through Why are you yelling so loudly?, and ends on Jiang Li's righteousness temporarily shut Jiang Yan.
If you want the clearest chapter reference, go to Chapter 38. Early on, Jiang Li had also observed the girl who had just entered.; later, the chapter leans on Before arriving, she had briefly reviewed the profiles of the other three....
If you want the clearest chapter reference, go to Chapter 8. Early on, The resentment that had barely calmed among the crowd surged back two...; later, the chapter leans on Some of them were relatives of the Jiang Family, who felt it improper to....
Chapter 1 is the strongest chapter-level answer because it starts from Jiang Li, I'm warning you, don't set your sights on Yinwan anymore, or... and follows through on Yet before she had the chance to teach her a lesson, the male lead arrived....