Making it not too cheesy or overly cutesy can be difficult. Since the idea of a character in diapers can easily go into the realm of being overly sentimental, the writer has to find the right balance between humor and maintaining the essence of the Sirius Black character.
Another challenge is to create a unique and engaging story within this rather unusual premise. There are limited examples in the original source material about Sirius as a baby, so the writer has to be creative in building a world around a diaper - wearing Sirius Black. For example, how does his family react to his early signs of magic while he's still in diapers? How does this shape his future personality? These are all aspects that need careful consideration.
One idea could be a humorous take on Sirius as a baby with his magical abilities already showing in unexpected ways while in diapers. For example, he might accidentally levitate his diaper when he gets excited.
One challenge is maintaining the essence of Peter Pan while he's in a baby state. Peter is usually known for his adventurous and free - spirited nature. When he's a baby in diapers, it's hard to show that same side of him in the same way.
The challenge also lies in the fact that you need to create a new narrative arc that involves Percy in diapers without deviating too much from the established mythology of the series. You have to think about how his demigod powers interact with his baby - like state in diapers. Do they change? Are they more difficult to control? And you need to do this in a way that is engaging for the readers who are used to the normal Percy Jackson adventures.
The main problem is that Sirius Black is from an older generation of wizards and has a very different set of values and experiences compared to Hermione. For example, Sirius was part of the Order of the Phoenix during the first wizarding war, while Hermione is dealing with the aftermath of the second wizarding war. Their perspectives on magic, society, and relationships are likely to be different. Moreover, Sirius has a rather dark past which might be hard to reconcile with Hermione's relatively sheltered Hogwarts life. It's a challenge to create a story where they can interact meaningfully without sacrificing the essence of either character.
One challenge is getting their personalities right. James is known to be brave, confident and a bit of a prankster, while Narcissa is from a more traditional and often dark - aligned family. So, it's difficult to make their interactions believable.
One big challenge would be their past history. They were enemies during their school days. Sirius and his friends bullied Snape, which created a deep-rooted hatred. Another challenge could be their different loyalties. Snape was initially on the side of the Death Eaters (though secretly a double - agent), and Sirius was a firm member of the Order of the Phoenix. These differences in their past associations could cause a lot of friction in their relationship.
One possible fanfiction could be set in a dark, abandoned castle where Sirius Black's shadowy figure lurks. His eyes glow menacingly in the dark, and every step he takes makes a creaking noise that sends shivers down the spines of those who hear it. The characters in the story might be a group of young witches and wizards who accidentally stumble upon this place and have to face their fear of Sirius Black.
A possible fanfiction plot could involve Sirius Black being a Sentinel and his Guide being a mysterious new student at Hogwarts. Their connection is immediate and strong. As they work together, they start to uncover secrets about the wizarding world that no one else knows. They face challenges from dark wizards who want to use Sirius' powers for their own evil purposes. Their relationship as Sentinel and Guide becomes a key element in their fight against the darkness, and their love story could also be intertwined in the plot.
One possible fanfiction idea could be that Sirius decides to cut his hair as a symbol of starting anew after escaping Azkaban. His long, shaggy hair was a part of his wild look, but now he wants to look more presentable to his friends and family. He might cut it in a simple yet stylish way, and his friends' reactions could range from shock to admiration.
To start writing a Sirius Black OC fanfiction, begin with your OC's concept. Consider their magical abilities. Are they a powerful animagus like Sirius? Or do they have some other unique gift? Once you have that sorted, plan out the setting. Will it be mainly in Grimmauld Place or outside in the wizarding world? As for the relationship with Sirius, you can start from an initial encounter. Say, your OC bumps into Sirius in Diagon Alley. From there, build up the story, adding in elements of the wizarding world's lore and some drama to keep the readers interested.