One idea could be exploring what would happen if the main character had to go back in time one more time to fix an unforeseen consequence of his previous time - traveling adventures. Maybe he discovers a new villain who was created as a result of his actions.
Another interesting fanfiction idea could be a 'what if' scenario where the Adam Project was a collaborative effort between different dimensions. So, characters from parallel universes come together to work on the project, leading to all kinds of chaos and new friendships.
One idea could be exploring Adam's adventures in an alternate universe. Maybe in this universe, he has to team up with a different version of himself to save the day. Another could be delving into his relationship with his mother before the events of the movie in a more in - depth way.
One idea could be exploring what would have happened if Adam and Eve had not eaten the forbidden fruit but instead found a way to communicate with God more directly to understand the purpose of the tree better. Another could be a fanfiction where they have different personalities than the traditional view, like Adam being more hesitant and Eve being the more adventurous one.
Perhaps in the fanfiction, Adam Levine has an accident that leaves him unconscious. A super - fan discovers a way to enter his mindscape while he's out. In there, she finds that his unconscious is filled with half - written songs, memories of his concerts, and his hopes for the future of his music career. She then tries to help him by organizing these elements in his mind, all while falling in love with the essence of who he is.
One idea could be a crossover with Superman. Imagine Black Adam's brute force against Superman's more noble strength. They could start as enemies but then be forced to team up against a greater threat like Darkseid. Another could be a crossover with Doctor Strange. The magic elements would be really cool to explore, with Black Adam's ancient magic clashing or combining with Strange's more esoteric sorcery.
One idea could be a story where the baby in the 'baby project' has some sort of special power that the characters have to figure out how to manage. Maybe the baby can communicate telepathically and it leads to all sorts of comical and heartwarming situations as the characters try to understand what the baby wants.
One idea could be to focus on the adventures of a unique pet in the Caeria world. For example, a magical pet that can communicate with different species. It could go on a journey to find a lost relic that has the power to save its home.
One idea could be Adam's backstory exploration. Maybe he had a different life before coming to the Hazbin Hotel universe and that could be delved into. For example, his family, his upbringing, and how those things might have shaped his current self.
Maybe they could go on a road trip together. Along the way, they discover new things about each other and their pasts. They might run into old friends or foes from their respective storylines, which could add drama and conflict to the fanfiction. For example, they could encounter someone who has a grudge against Adam and Chelsea has to decide whether to stand by him or not.
Well, a really interesting plot could be that Prince Adam's curse starts to affect Belle in some strange way, like she starts to have visions of his past. Then they have to figure out how to stop this new development. Also, they could go on a journey to find a long - lost relative of Adam's who might have a way to break the curse completely. And there could be a part where they face a magical being who tests their love for each other in unexpected ways.
One interesting plot idea could be that Lucifer, seeing Adam's pure and innocent nature, decides to test him in various ways. He might create illusions of worldly temptations to see if Adam can resist. Another could be that Adam, being curious about the fallen angel, tries to understand Lucifer's fall from grace and in the process, they form an unlikely friendship that challenges the norms of heaven and earth.