Danny might react with panic at first. After all, he has been hiding his identity from his parents for so long. He could try to escape from them, using his ghost powers in a desperate attempt to get away before they can do anything drastic.
In some fanfictions, Danny Phantom may hate his parents because they are constantly trying to hunt him down. His parents are ghost hunters and they don't know that Danny is actually half - ghost. So their actions of trying to capture and study ghosts put Danny in a dangerous and uncomfortable position, which could lead to feelings of hatred.
Yes, there are some. You can usually find them on fanfiction websites. Just search for 'Fem Danny Phantom Hates Christmas' on popular fanfic platforms.
The plot could involve a villain who specifically targeted Danny's parents to get to Danny. After their death, Danny is filled with anger and a thirst for revenge. He has to balance this new - found rage with his responsibilities as a half - ghost and as a son who wants to honor his parents' memory by protecting the town they loved.
Perhaps Danny's friends find out that he has been caught by his parents. They could come to his rescue. Tucker might use his tech - savvy skills to hack into the Fenton's security systems, and Sam could try to reason with Danny's parents. Together, they could try to convince Danny's parents that Danny is still the same person they love, just with some extraordinary powers.
In the fanfiction, the fem Danny Phantom might hate Christmas because it represents a time when she feels most different. If she's a half - ghost, Christmas might be a time when she's acutely aware of not fitting in with either the human or the ghost world. All the normal human traditions and the special 'ghostly' events during Christmas might make her feel isolated. For example, humans are busy with their family dinners and gift - giving, while ghosts might have their own spooky celebrations. She, being in between, has nowhere to belong during this time, thus leading to her hatred for Christmas.
One way is to focus on Danny's emotional journey. Show his initial shock and disbelief. For example, he might find it hard to accept that his parents, who were always so full of life in their ghost - hunting adventures, are suddenly gone. This could lead to him feeling isolated as he tries to deal with this loss on his own.
One possible scenario is when his parents accidentally harm one of his ghost friends while trying to hunt ghosts. Danny might get really angry and show his hatred towards them for being so reckless. Another scenario could be during a family dinner when they start talking about their latest ghost - hunting inventions and how they plan to use them to catch more ghosts. Danny, feeling threatened by this, could snap and show his dislike for them.
One idea could be exploring how Danny's parents react when they finally discover his ghost - hunting powers are actually related to his own ghostly nature. Maybe they initially feel betrayed but then come to accept it.
One motive could be to get leverage over Danny. By holding his parents hostage, Vlad can try to force Danny to do things for him, like joining him or handing over his ghost powers.