The main character, Judson Cross, is often a popular choice. His leadership skills and vast knowledge make him a great centerpiece for a story. Another one is Sydney Fox. Her bravery and determination are very appealing, so it's easy to build stories around her.
Well, you could write a fanfic where the Adventure Inc team gets separated in a large, maze - like underground cavern. Each member has to use their individual skills to find their way back to the others while also uncovering secrets of the place. This would add a lot of tension and character development as they face their own challenges alone.
I'm not entirely sure what 'black inc fanfic' specifically entails. It could be that there is a particular group or community that uses this term. It might be related to a specific genre of fanfiction. Maybe it has something to do with a certain type of business or organization in the fictional realm. If it's a small - scale or niche thing, it could be that only a select group of fans are familiar with it and create content for it. It could also be that the 'Black Inc' has some sort of unique or interesting backstory that the fanfic delves into.
Another idea is that all the characters are now parents themselves. They have to balance their work at Monsters Inc with raising their own little monsters. It could show how they use their experiences as scared kids or scarers to be better parents.
Friendship is a very common theme. Since the OC is a new character, often the story focuses on how they become friends with Sulley. For example, they might help each other out in tricky situations at Monster Inc.
Sorry, I'm not familiar enough with 'black inc fanfic' to recommend any specific ones. You could try searching on fanfiction platforms or relevant forums where fans might discuss and share their works related to 'Black Inc'.
In an all - grown - up Monsters Inc fanfic, the world itself could have evolved. There could be new technologies for scaring or collecting energy. The characters might have to adapt to these changes. And if Boo is all grown up and involved, she could bring a human perspective that helps the monsters improve their scaring business in unexpected ways. Maybe she could introduce new concepts from the human world that the monsters had never thought of, like different ways of using sounds or lights for scaring.
It could be about Boo using her experiences in the monster world to make a difference in the human world. Maybe she becomes an advocate for better understanding between humans and monsters.