Well, in such a fanfiction, it could be due to various reasons. Maybe Ochako realizes that their hero paths are leading them in different directions. It might also be a plot device to create more drama and character development for both Deku and Ochako.
It's mainly because of their great chemistry in the original series. They are friends and classmates, and there are moments that hint at a possible deeper relationship, which fans love to explore in fanfictions.
One great Deku x Ochako fanfiction could be 'A Shared Dream'. In it, they train together and slowly realize their feelings for each other during a difficult mission. Another is 'The Unspoken Bond' which focuses on how they support each other through tough times at school.
For Ochako, she might face some backlash from their mutual friends. They might not understand her decision at first. But she could focus on her own hero journey more intently. Maybe she'll start taking on more challenging missions to prove that she made the right choice. And as for their relationship, there could be a chance for reconciliation later in the story if the writer decides to go that route. It all depends on how the characters are developed further.
One good Ochako jealous fanfiction is 'Green-Eyed Uravity'. In this story, Ochako gets jealous when Deku spends a lot of time with a new female hero in training. It really delves into her feelings of insecurity and how she tries to deal with them. The author does a great job of portraying Ochako's character.
Growth is also a key theme. Through experiencing jealousy, Ochako has the opportunity to grow as a person. She learns to better understand her emotions, control her jealousy, and become more confident in herself and her relationships. This is often shown as she overcomes her jealous tendencies and becomes a stronger person both emotionally and in her hero work.
There's also 'Growth Together'. This fanfic shows how Deku and Todoroki support each other during tough times at UA. They face challenges not only from villains but also from within the school. Their relationship develops as they help each other overcome these obstacles.
One idea for a Deku's Quirk fanfiction could be exploring what would happen if Deku's quirk manifested in a different way. For example, instead of having to gradually control One For All, he suddenly has full mastery from the start. This could lead to a very different story arc where he is immediately seen as a top - tier hero - in - training, causing envy and admiration in equal measure among his classmates.