It could be a long - lost relative of Harry's. Maybe it's a distant cousin whose family was lost during the wizarding wars. Harry finding the baby would then be a way to reconnect with his family roots and also protect the family line. Since Harry has lost so many of his own family members, he would be very determined to keep this baby safe.
The baby could be the child of a minor character from the original series who was in hiding. For example, the baby might be the offspring of a wizard who was on the run from Voldemort's followers and unfortunately didn't make it, leaving the baby behind for Harry to find.
The baby could be an alien species that Goku has never encountered before. It might have special powers related to its alien origin, like the ability to control energy in a different way than Goku and his friends.
The baby could be an ordinary human baby that has some sort of latent magical ability that Raven senses. She then decides to protect the baby from the human world that may not understand or accept the baby's potential magic, and also from the magical world that might want to exploit the baby.
The baby could be an orphan from a nearby village that has been attacked. Kagome stumbles upon the baby while on her travels with Inuyasha. Since she has a big heart, she can't just leave the baby there, so she takes it with her.
The baby could be a lost elf child from a different part of the forest. Maybe their family was attacked by some dark force and Thranduil finds them by chance.
The baby could be a half - demon, related to some other important character in the series. Maybe it's the offspring of a character Sesshomaru has some history with.
Well, perhaps in this fanfiction, Harry Potter stumbles upon a baby while on one of his adventures. Maybe the baby has some sort of magical power that he has to protect from the dark forces. It could also be that the baby is related to an old prophecy and Harry has to figure out how to keep it safe and fulfill the prophecy at the same time.
Maybe the baby is a result of some sort of magical experiment gone wrong. And Harry Potter finds it in a hidden place where the experiment was carried out. The baby might have some strange and unpredictable magical abilities as a consequence.
There could be many potential authors. It might be a fan who loves the character of Dean and wanted to create a unique story around him finding a baby. It could be someone who is new to fanfiction writing and thought this would be an interesting scenario to explore.
The author could be anyone. It might be a fan who has been following the story of Zuko for a long time and thought it would be interesting to write a story where he finds a baby. It could also be someone who was inspired by other fanfictions or the original story and decided to put their own spin on it with this concept of Zuko finding a baby.
It could also be a group of fans who collaborated on the fanfiction. Each person might have contributed different ideas, like one coming up with the concept of Itachi finding the baby, another thinking about the setting, and someone else planning out how Itachi would interact with the baby in the story.