One interesting aspect could be the exploration of Casper's character in a human form. It might involve new relationships and character development that are unique to his human state.
It could be another ghost who is jealous of Casper's new human form. This ghost might try to sabotage Casper's attempts to fit into the human world, perhaps by causing chaos around him and making humans afraid of him again.
I don't have a list of 'casper is human fanfiction' to recommend. You could try searching on fanfiction websites using relevant keywords like 'casper human' to find some good ones.
One idea could be that Casper has to learn about human emotions in a very short time. For example, he might experience love at first sight with a human girl and then struggle to understand jealousy when he sees her with another boy.
A really good Casper story could involve Casper helping a group of lost travelers find their way out of a dark and confusing forest. Casper used his knowledge of the spooky area to guide them. He led them through the thick fog and strange noises until they reached safety. Casper's helpfulness in this story makes it a great one.
I'm not sure which specific 'Casper real story' you are referring to. There could be many stories related to something named Casper. It could be about a person named Casper, a Casper in a particular town's history, or perhaps a Casper in a fictional world that has some real - life inspired elements.
An old caretaker of the haunted house where Casper lives. He's a bit gruff on the outside but has a soft heart. He knows about Casper's existence and has a sort of unspoken agreement with him. He could offer wisdom and help to Casper when he gets into trouble with his ghostly powers.