She could be an ordinary girl who just happened to be at the right place at the right time and caught Izuku's eye. Maybe she was at a hero event and Izuku noticed her kindness towards the other attendees.
The girl might be a new hero - in - training at UA. She could be in a different class from Izuku, and they start dating secretly because they don't want to cause a stir among their classmates. She could have a really unique quirk that Izuku is fascinated by.
In the 'izuku secretly dating a girl fanfic', the plot could be that the girl is actually from a rival school. Izuku is initially hesitant about the relationship because of the potential conflict of interest. But their feelings for each other are too strong. They date secretly, and there could be some close calls where they almost get caught by classmates or teachers from either school.
It could be a character who somehow discovers Izuku's secret and tries to use it against her. Maybe a rival at school who is jealous of Izuku's progress and sees this as a way to get her expelled or discredited in the hero community.
Maybe the story could focus on how Izuku, as a girl secretly, has different perspectives and experiences compared to her male counterparts. She might face unique challenges in a male - dominated hero society, like having to prove herself even more. And there could be a sub - plot about her developing a romantic interest in another character, but being hesitant because of her secret.
Perhaps a jealous classmate who has always been in Izuku's shadow. Now that Izuku is a girl, this classmate sees an opportunity to undermine her. They spread rumors about how Izuku's transformation is some sort of cheat or that she's not the same reliable person she was as a boy. This classmate's actions and attempts to sabotage Izuku would make them the main antagonist.
Perhaps a rival adventurer who discovers Bilbo's secret and tries to use it against her. This antagonist could be jealous of Bilbo's place in the group and sees her secret as a way to undermine her and take her position. He might spread rumors or try to create situations where Bilbo's secret is likely to be revealed.
Izuku might become more self - conscious about her appearance in this fanfiction. Since she is a girl, she could face different beauty standards, which may influence her confidence in different ways compared to when she was male - presenting in the original story.
Well, it could start with Izuku waking up as a girl one morning with no explanation. He (now she) tries to keep it a secret at first but then realizes it's not possible. The story could focus on how Izuku's relationships change. For example, Bakugo might initially tease her more harshly but then come to respect her in a different way. And Midoriya could find that she has a different approach to using her quirk as a girl, maybe being more strategic or having different physical capabilities that she has to learn to master.
In the 'izuku becomes a girl fanfic', perhaps the plot involves Izuku adjusting to her new physical form. She might struggle with things like different clothing styles and how society views girls in the hero world. Also, her relationship with other characters could change. Her friendship with Ochaco might become more complex as they now have more in common as girls. And Bakugo might react in a really interesting way, either being more protective or even more competitive towards her.
The plot could involve Gaara trying to hide her gender while still being a powerful shinobi. Maybe she has to constantly worry about being discovered during battles or in interactions with other ninja. For instance, she might have to come up with excuses for not sharing certain spaces with male ninja.
Well, perhaps the plot could involve Bilbo hiding her true gender identity in a world where being a girl might bring unexpected challenges or opportunities. Maybe she has to keep it a secret to be able to go on adventures like the male hobbits do. She could be constantly worried about being discovered while also having to deal with her own self - discovery and acceptance of her femininity.