Well, one way it could occur in fanfiction is if there's a magical artifact involved. Suppose there's an ancient magical object that has the power to create life when two people with strong magic, like Hermione and Fleur, interact with it. Another possibility is that a powerful magical being decides to play a trick on them and creates this baby situation as a way to teach them a lesson or to set off a series of events in the fanfiction world.
In some fanfictions, it might be due to a parallel universe or dimension - related event. For example, Hermione and Fleur could be transported to a different dimension where the rules of magic are a bit different. In this new place, the magic that exists between them could lead to the creation of a baby. It could also be that a prophecy in the fanfiction world predicts that they will have a child together, and the fanfiction then builds a story around how this prophecy comes to pass.
In some fanfictions, Hermione might get involved in a magical mishap during the wedding. Maybe she accidentally casts a spell that causes some chaos among the guests, like making the flower arrangements come to life and start chasing people around. It could also be that she discovers a secret plot against the newlyweds during the wedding festivities.
Their friendship could start during an inter - school event. They might be paired up for a task, like a magical dueling tournament or a collaborative spell - casting project. At first, they might be a bit competitive, but then realize they can achieve more together. For instance, Hermione's quick spell - casting and Fleur's grace in magic could complement each other.
Well, one possibility is that Fleur could be really surprised at first. Maybe she'd initially be hesitant because she might have had other plans or expectations for the Yule Ball. But then, she could see Hermione's earnestness and decide to go with her. They could end up having a great time, dancing and chatting, and maybe even become closer friends through this experience.
The baby would likely be very intelligent, considering Hermione's brilliant mind. It might inherit her love for books and knowledge. Also, given Fleur's Veela heritage, the baby could be extremely beautiful with an almost otherworldly charm.
One possible plot could be that the baby has unique magical abilities. Since Harry has his own set of powerful magic and Fleur is part Veela, their baby might inherit a combination. Maybe the baby can communicate with magical creatures in a special way, leading to adventures where they all have to protect the baby from those who might want to use its powers for evil.
One possible plot could be that Hermione, as a Lycan, struggles to hide her identity within the Hogwarts community. Fleur, being perceptive, might notice something off about Hermione. Maybe Hermione is afraid of being discovered and ostracized, while Fleur, having her own experiences with being different (as a Veela), tries to help Hermione come to terms with her new lycanthropy. They could form a strong bond as they both deal with the challenges of being 'other' in the wizarding world.
They could face opposition from some in their community who don't accept their relationship or the idea of them having a baby. But Nico and Will would stand strong together.
It could be developed by having Fleur first struggle with her feelings internally. She might be confused because it's not a common type of attraction in the wizarding world. For example, she could write in a diary about her feelings for Hermione.
One possible plot could be a story set during a Triwizard Tournament - related event. Maybe Fleur and Hermione are forced to work together in a dangerous task and during a moment of panic or urgency, Fleur straddles Hermione to protect her from some sort of threat. And from there, a new bond forms between them.
A possible fanfiction plot could involve Hermione and Fleur working together to solve a mystery in the wizarding world. Maybe there is a series of strange magical occurrences that are baffling the wizarding community. Hermione's logical thinking and Fleur's intuition could combine to crack the case. Along the way, they learn about each other's strengths and weaknesses, and their relationship blossoms into a true partnership where they rely on each other and value each other's contributions.