One possible plotline could be that Danny gets into a fight with a new and extremely powerful ghost. This ghost has some sort of unique power that can cause severe harm to Danny, like a draining ability that saps his energy and leaves him severely injured. He then has to struggle to hide his condition from his friends and family while trying to find a way to defeat the ghost.
Maybe Danny is exposed to some sort of toxic ectoplasm that severely damages his ghost half. This causes him to lose some of his powers and he has to deal with the physical and mental pain. His friends notice his strange behavior and start to suspect something is wrong. Danny has to decide whether to tell them the truth or try to handle it on his own while he's in a weakened state.
In another plotline, Danny could be caught in a trap set by a group of ghosts who are out for revenge. The trap is designed to cause maximum harm to him. He gets severely hurt and is stranded in the Ghost Zone. He has to use his wits and any remaining strength to find a way back home and also figure out how to get revenge on those who hurt him.
One common theme is the struggle of recovery. Danny has to deal with physical and emotional pain as he tries to heal from his severe injuries. Another theme could be the importance of friendship. His friends might come together to help him, showing that their bond is strong.
One possible plotline could be that Desiree, with her wish - granting powers, accidentally makes Danny Phantom her ward while trying to fulfill some other self - centered wish. As she raises him, Danny has to constantly struggle with the fact that Desiree's motives are often not pure. For example, she might try to use Danny to gain more power or influence in the Ghost Zone.
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 possible scenario could be Danny getting bullied at school. Maybe some of the other students find out about his ghost powers and they target him out of fear or jealousy. Another could be that he gets injured during a ghost attack that takes place on school grounds while he's trying to protect his classmates.
One possible plotline could be Danny trying to hide his sickness from his enemies while still fighting ghosts. He might be weaker than usual, but his determination keeps him going.
A Danny Phantom hurt fanfiction could involve Danny getting hurt while exploring a new, dangerous part of the Ghost Zone. He might encounter some sort of toxic energy or a trap set by an evil ghost. His pain and struggle to get back to safety could be the main focus, and how he overcomes his injuries could show his strength and determination.
A plotline might involve Vlad trying to isolate Danny from his friends and family in the fanfiction. By doing so, he can have more control over Danny and make him more vulnerable to his abuse. This could lead to Danny having to find ways to break free from this isolation and seek help.
In a Danny Phantom fanfiction about Danny being controlled, it might be due to an ancient ghost spell. Some evil ghosts find an old spellbook and use it on Danny. This could lead to Danny having to fight against the control from within himself. His friends, like Sam and Tucker, would then have to find a way to break the spell. They might search for a counter - spell in the Ghost Zone or consult other friendly ghosts for help.
Well, in some fanfictions, it could be that Lucy is under a curse. This curse makes her act out of character and she ends up hurting Natsu. Maybe she is cursed to attack the closest person to her, and at that moment, it's Natsu. Or it could be a situation where Lucy is forced to choose between saving herself and Natsu in a dangerous situation, and her choice, even if it's to save herself, could be seen as hurting Natsu. Also, there could be a plot where Lucy is brainwashed by an enemy who wants to break the bond between her and Natsu, and as a result, she causes him harm.
A plotline could be that Hana is jealous of Naruto's popularity or power. So, she decides to challenge him and in the heat of the battle, she ends up hurting him. Naruto, on the other hand, is shocked by her actions and tries to talk to her to find out why she did it. This could then turn into a story about friendship and forgiveness, as Naruto may choose to forgive Hana and help her overcome her jealousy issues.