A common theme is the struggle between good and evil within Danny himself. Since Dark Danny is Danny's dark side personified, it's all about Danny facing his own inner demons. For example, in many fanfictions, Danny has to deal with the temptation to give in to the power that Dark Danny represents.
One great piece of Danny Phantom vs Dark Danny fanfiction is 'The Battle for Souls'. It really delves into the psychological struggle between the two. The author does an amazing job of showing Danny's inner turmoil as he faces his dark counterpart. It's full of intense action scenes and deep character exploration.
Danny's relationships change drastically. He distances himself from his friends and family. He no longer values their opinions or support. Instead, he might see them as obstacles or even threats. His friendships with Sam and Tucker are strained as he starts to engage in activities that they find morally wrong, like using excessive force on other ghosts or humans who get in his way.
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.
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 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.
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.
One great Danny Phantom Danny Fenton fanfiction is 'Phantom's Memories'. It delves deep into Danny's dual identity struggles in a really engaging way. The author does an amazing job of portraying Danny's emotions as he tries to balance his normal life as Danny Fenton and his heroic duties as Danny Phantom. Another good one is 'Fenton's Secret Revealed'. It takes a different turn by exploring how the people around Danny react when they start to suspect his secret. This fanfiction is full of suspense and keeps you on the edge of your seat.
In a Danny Phantom trans girl fanfiction, Danny could discover her true identity as a trans girl after an encounter with a special ghost. This ghost could be like a spirit guide that shows her visions of who she really is. Danny then has to figure out how to balance her newfound identity with her ghost - fighting duties. She may also have to deal with the reactions of her family, especially her parents who might be initially confused but eventually come around.
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.