His betrayal would likely be the catalyst for a whole new set of story arcs. Other characters might start to question their own loyalties. And since it's a 'lemon' fanfiction, there could be a sense of bitterness that spreads throughout the story. Maybe the town that Danny protects would also start to turn on him, thinking he can't be trusted anymore. It would be a downward spiral for Danny's character, at least initially, as he has to deal with the consequences of his actions.
The plot of 'Danny Phantom Betrayed Lemon' fanfiction might involve Danny being forced to betray someone against his will. Maybe he's under a spell or some form of mind control. The 'lemon' aspect could be related to how this betrayal leaves a sour taste in the mouths of the other characters. They might struggle to come to terms with what Danny has done, and there could be a long journey of forgiveness or revenge in the story.
His powers could become more ice - based. Instead of the normal greenish - blue energy, his blasts might turn a frosty white. His ability to fly could also be affected, with a cold trail following him as he moves through the air.
In a fanfiction, Maddie could be working on a project that involves Lemon. Danny, being curious, sneaks in to check it out. This leads to a series of events where they all have to work together to solve a mystery. For example, the mystery could be about a strange energy source that is affecting the town and Lemon has some knowledge about it from her own experiences.
In some fanfictions, Danny's mom might find out when she accidentally witnesses Danny transforming into his ghost form. Maybe she walks in on him at a crucial moment.
His ghost - hunting parents could potentially betray him. If they found out Danny was half - ghost, they might see him as a threat to humanity rather than their son. They've been so dedicated to hunting ghosts that their views could be clouded, and they might not be able to accept Danny for what he is, leading to a heartbreaking betrayal for Danny.
Danny would probably be heartbroken. He really cares about Sam, so finding out she cheated would be a huge blow. He might go into a state of denial at first, not wanting to believe it.
The plot could change in terms of her love interests. Instead of the typical male - led romantic arcs, there could be new female - centered ones. For example, she might have a different type of relationship with a male character, where she takes the lead more often.
In a crossover, characters from the other franchise might betray Danny. For example, if it's a crossover with a show about vampires, a vampire character who seems friendly at first could betray Danny for his ghost powers. They might want to use his powers for their own dark purposes. Another likely candidate could be a character who is jealous of Danny's abilities. Maybe in a crossover with a superhero world, a sidekick who feels overshadowed by Danny's powers and popularity might be the one to betray him.
It could be Valerie. She has had a somewhat rocky relationship with Danny in the original series. In a fanfiction about betrayal, she might be pushed over the edge by jealousy or a misunderstanding about Danny's powers and his intentions. She could then use her ghost - hunting skills against Danny in a more malicious way than before.
The original Danny Phantom story mainly focuses on his ghost - fighting adventures and his struggle to balance his normal life and his superhero identity. In contrast, the diaper fanfiction adds an entirely new and rather odd element. It takes the story in a direction that the original never did, focusing on situations related to the diaper which are not part of the core themes of the original.