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 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.
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.
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.
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.
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.
In most cases, if the fanfiction is not being sold or used in a way that directly competes with the original work, it's usually okay to read. But if the lemon content involves violating any laws such as those related to obscenity, then it's not legal regardless of it being fanfiction. Also, different countries have different laws regarding these matters.
One idea could be that Danny's friends turn on him because they believe false rumors spread by a new villain in town. Maybe the villain makes it look like Danny is using his powers for evil. Another could be that the government agency that was once somewhat friendly to Danny decides he's too dangerous and betrays his trust by trying to capture him.
Perhaps in the fanfiction, Danny is betrayed by a new ally he trusted. This new character could have joined Danny in his fight against evil ghosts, but in reality, they were working for a more powerful and evil ghost all along. They might use Danny's trust to learn about his weaknesses and then expose him to danger, leaving Danny feeling hurt and alone, having to reevaluate who he can trust in the future.
One possible scenario could be that Sam betrays Danny's secret identity to someone he doesn't trust, like a ghost hunter. Maybe she does it out of jealousy if Danny starts getting closer to another character.