In some fanfictions, it could be a character from another magical school. Like a girl from Beauxbatons or Durmstrang. She might have met Harry during an international magical event and they've been secretly seeing each other ever since.
It could be a Muggle - born witch who he meets outside of Hogwarts during the summer holidays. She's not part of the typical wizarding society he's used to, so they keep it a secret as it's an unusual situation for a wizard like Harry to be involved with a Muggle - born in such a way.
Well, maybe the story could be about how Harry meets this girl in a hidden corner of Hogwarts, perhaps in the Forbidden Forest during one of his adventures. They start to secretly exchange letters and meet in the dead of night. They keep their relationship under wraps because they fear how their friends and the wizarding world might react.
It could be Misty. They have a long - standing relationship in the Pokemon series. They've traveled together and shared many adventures, so in a fanfiction, it's not a stretch to imagine her as a secret girlfriend.
Maybe it's a new character created specifically for the fanfiction. A girl from a far - off region who Ash meets during one of his journeys. She could be a powerful trainer or have some special abilities that draw Ash to her, and they start a secret relationship.
The idea of Percy having a secret girlfriend in fanfiction can open up a whole new world of character development. If his girlfriend is a new character introduced in the fanfiction, she could have unique powers or abilities that complement Percy's. Their secret relationship could be a way to explore Percy's more private and vulnerable side, away from his usual heroic adventures.
There could be an original character created just for the fanfiction to be Harry's secret girlfriend. Writers often introduce new characters to add new plotlines and romantic interests for the main characters.
His secret girlfriend could be in a difficult situation herself. Maybe she's a demigod with a dangerous family or past. Percy is trying to help her while keeping their relationship a secret. This could involve them sneaking around to meet, sharing secret glances in public, and having to communicate in coded ways. It would create a really interesting and suspenseful plot.
It could be that the wizarding world has some sort of social or political situation where their relationship is not allowed or frowned upon. For instance, if she is from a family with a different magical ideology, and Harry doesn't want to cause a stir in the wizarding community. So they keep it a secret.
Another scenario could be that they start off as friends or classmates and gradually develop feelings for each other without realizing it at first. Then they keep it a secret because they are not sure how the other person really feels or they are afraid of ruining their friendship. In this case, there could be a lot of internal monologues and awkward moments between them in the fanfiction.