There's a fanfic titled 'Merged Realms'. It's a long - form fanfic that delves deep into the lore of both 'Black Butler' and 'Pandora Hearts'. The story starts off with a strange event that seems to connect the two worlds. As it progresses, we see the characters from both sides having to deal with new threats and challenges that are a result of this merging. It's really engaging and has some great fan - created art associated with it on some fanfic websites.
Another option is Tumblr. There are often fanfic recs (recommendations) on Tumblr blogs dedicated to 'Black Butler' or 'Pandora Hearts'. Some users also post their own short fanfics directly on their blogs. You can use Tumblr's search function to look for relevant tags such as '#BlackButlerPandoraHeartsFanfic' to find these posts. It's a bit different from the more formal fanfic platforms, but it can be a great source for finding unique and interesting fan - created stories.
Oz Vessalius is a great character to feature. His complex backstory, including his connection to the Abyss, gives a lot of room for exploration in a fanfic. Another good one is Alice. Her brash and often unpredictable nature can add a lot of interesting twists to a story. Also, Gilbert is a character full of loyalty and internal conflict, which can be used to create engaging storylines.
One idea could be a fanfic that focuses on the backstories of the minor characters in Pandora Hearts. For example, exploring the past of some of the servants in the Vessalius household. Another idea is a time - travel fanfic where a character goes back in time to change a crucial event in the Pandora Hearts story. Maybe a fanfic that imagines an alternate ending to the series, where different alliances are formed and different fates await the characters.
Another place could be FanFiction.net. However, the quality and content can vary greatly. It's important to read the tags and summaries carefully to find the ones that focus on the relationship between Alice and Break in Pandora Hearts. Some fanfics might be more centered around action or other aspects of the story, so you need to be a bit picky.
A very interesting one is 'Beyond Duty'. In this fanfic, it shows how Vincent and Gil's relationship goes beyond their respective duties in the Pandora Hearts universe. It has a lot of character development for both of them and shows how their bond can withstand different challenges and trials.
One great fanfic is 'A Bond Beyond Time'. It beautifully explores the relationship between Gil and Oz. The author does a wonderful job of capturing their personalities and the unique bond they share. It has some really touching moments that make you feel the depth of their connection.
You could make an OC that is a half - human, half - Chain. This OC would struggle with their identity, being shunned by both humans and Chains. Their story could revolve around finding their place in the world of Pandora Hearts. They might have special abilities that neither humans nor Chains possess, which could make them a target for various factions in the story. They could also form an unlikely alliance with some of the main characters who see their potential and uniqueness.