Over time, if he continues not to eat, his health could deteriorate. His body could become more vulnerable to diseases and other physical ailments. This would not only be a problem for him as a human but could also potentially affect his ability to use his ghost powers since his human and ghost sides are intertwined in some ways.
His concentration might be affected. Lack of food can lead to a lack of focus. Danny needs to be sharp when dealing with the various threats in Amity Park. If he's not eating, he might make more mistakes during battles or while trying to solve problems related to the ghosts.
He could start to lose strength. Food provides the energy needed for normal human activities, and even though Danny has ghost powers, his human side still needs proper nourishment. Without eating, he might find it harder to fight ghosts effectively as his physical strength wanes.
Another possibility is that he's facing some emotional turmoil. Danny has a lot on his plate. He has to keep his identity a secret from his friends and family, deal with school, and fight ghosts. All this stress could be causing him to lose his appetite. He might be too worried or preoccupied to even think about food.
One possible storyline could be that Sam is influenced by a new, mysterious character in town. This character might be using some sort of mind - control or persuasion power on Sam, making her act out of character and cheat on Danny. Another idea is that Sam and Danny have a big fight over Danny's ghost - hunting duties. Sam feels neglected and in a moment of weakness, she might get involved with someone else.
One possible storyline could be that Danny is pushed to the edge by constant bullying at school and the stress of hiding his ghost powers. This leads him to gradually embrace the darker side of his powers and become Dark Danny. For example, Dash's continuous taunts and the school's overall negative attitude towards him make him lose faith in humanity.
In this fanfiction, it could be that Danny Phantom meets a Danny Phantom from a parallel fan - made story. At first, they don't trust each other. But as they learn more about each other's worlds, they realize that there are some common elements that are being threatened. It could be that a powerful ghost is trying to rewrite all the fanfic universes related to Danny Phantom. So, they must combine their strengths and knowledge to stop this from happening.
Well, in this kind of fanfiction, Danny could be controlled by an ectoplasmic parasite. The parasite latches onto Danny and takes over his actions. His eyes might glow a different color to show he's not in control. His friends would first be confused, then realize something is amiss and start investigating.
One possible story could be that Danny is facing a new and extremely powerful ghost. He needs help from his friends Tucker and Sam. Maybe they need to find a rare artifact to defeat this ghost. They could start by researching in the local library, looking through old ghost lore books. Tucker uses his tech skills to try and track down any leads on the artifact's location, while Sam uses her knowledge of the occult.
Confident Danny in fanfiction often shows leadership. He's not afraid to take charge and guide his friends in ghost - hunting adventures. He might make decisions quickly and firmly, like deciding on the best strategy to defeat a powerful ghost. His confidence gives others the reassurance to follow him.
One possible plotline could be Danny getting transported to the Naruto universe and somehow obtaining the Sharingan. He then has to learn to use it while still having his ghost powers, which could lead to some really cool battles against Naruto - universe villains.
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.
One interesting story could be about Danny and Sam going on a ghost - hunting adventure together. They might discover a new type of ghost that has unique powers and they have to figure out how to defeat it using their combined skills.