Well, in some Danny Phantom daddy fanfiction, the focus could be on how Danny's father reacts to the various ghostly events that happen around town. Maybe he starts to believe in the supernatural more quickly than in the original series and tries to help Danny protect the town from the ghosts in his own way. This can lead to some really heartwarming or action - packed stories.
There are some fanfictions that focus on Danny's daddy being involved in his adventures in the Ghost Zone. This could include scenarios where his father teams up with Danny to fight a powerful ghost, adding an interesting twist to the typical storylines. It might also explore how their relationship changes as they face challenges together.
One interesting story could be about Danny's dad finding out about his Phantom identity in a really emotional way. Maybe he discovers it by accident while trying to fix some of his ghost - hunting equipment.
There's also 'Daddy's Little Ghost'. In this fanfiction, Danny has to deal with the challenges of raising a daughter who has started to show signs of having ghostly powers like him. It's really interesting to see how he imparts his wisdom and experiences to her.
One great Danny Phantom and Danielle Phantom fanfiction is 'The Twin's Adventure'. It explores their relationship in a new ghost - fighting scenario. Another is 'Danielle's Discovery' which delves into Danielle finding out more about her powers and her connection to Danny.
One idea could be that Danny's ghost powers somehow lead to an unexpected pregnancy situation for a female character, and then he has to deal with the responsibilities of being a 'baby daddy' while still keeping his ghost - fighting a secret. For example, maybe a new ghostly enemy targets the unborn child.
Obviously, Danny Phantom himself could be the 'baby daddy'. His dual nature as a human and a ghost could bring a lot of interesting twists to the story of having a baby. For instance, the baby might inherit some of his ghost powers, which would create all kinds of challenges for raising the child.
You can try websites like Archive of Our Own (AO3). It has a large collection of fanfictions, and you can search for 'daddy Danny Phantom' specifically to find relevant stories.
One common theme is protection. Danny, as a father, is often portrayed as trying to protect his daughter from the various threats in the Danny Phantom universe, whether it be other ghosts or the secrecy of his own past as a half - ghost.
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.
One great story could be 'The Sibling Bond' where Danny and Jazz face a new ghost threat together. In this fic, their relationship is explored deeper as they rely on each other in the face of danger.
One great one to start with could be 'The Ghostly Guardian'. It really delves into Danny's growth as a hero. Another good option is 'Phantom's New Beginnings' which gives an interesting take on his relationships. And 'Danny's Secret Allies' is also quite engaging as it introduces some new and unique characters.