I'm not sure specifically as there could be many different 'a light in the cupboard' fanfictions. It might be about a mysterious light found in a cupboard, perhaps leading to a magical or unknown world, or it could be related to a character finding something special in the cupboard that the light reveals.
There's no way to know precisely without reading the fanfiction. However, it's common for fanfictions to feature existing characters from a related franchise if it's a fan - based work. If it's an original fanfiction, it could have a unique set of characters. Maybe there's an inventor type who tries to figure out how the light works, or a curious explorer who wants to follow the light wherever it leads.
There might be a fanfiction where the cupboard is a place of solace for Harry. Instead of being a place of punishment, it becomes his secret hideaway. He could decorate it with magic and use it as a place to practice spells without the Dursleys noticing. He might also find a magical creature living in the cupboard that becomes his friend and helps him through difficult times at the Dursleys'.
A cupboard love story could be about a love that is somehow related to a cupboard. Maybe it's a story where two people meet while hiding in a cupboard, or perhaps there is a special item in the cupboard that brings two characters together in a loving way.
Hermione would probably be very interested in the modified cupboard. She might study how Harry used his magic to make the modifications and offer some suggestions to improve it, like adding a spell - based locking mechanism that only responds to certain magical phrases.
Well, it's a very strange concept. Maybe in this fanfiction, some sort of magic gone wrong causes Harry to have the ability to give birth, and the cupboard could be a significant place because it was his initial living space in the Dursleys' house. It might be a really wild exploration of magic and gender roles within the Harry Potter universe.
It could be a storage for ancient and dark artifacts. A group of dark wizards are after these artifacts stored in the cupboard, and Harry has to protect it. This could lead to an epic battle between Harry and the dark wizards right in his old home in Privet Drive.
Well, it's Harry Potter and Ginny Weasley. Harry is known for his adventures throughout the wizarding world, and Ginny has always been a strong - willed character. In this fanfiction, they are the ones whose relationship is explored while they are in the broom cupboard. It could be about their private moments, conversations, or even some sort of magical discovery they make together in there.
I'm not entirely sure specifically which 'girl in the cupboard story' you mean. There could be various stories with such a title. It could be about a girl who hides in a cupboard for safety, perhaps from some kind of danger in the house like an intruder or a natural disaster.