Jade-Casper relationship

"Cade" or "Jasper" is the best friend/sibling relationship between siblings Jade and Casper.

Comics
In the comics, they first meet in Brothers and Sisters. Both of them learn they are twins through their parents. He saves her life from drowning and is welcomed into the Ghostly Trio's household because Jade is their brother's daughter.

Points in the comics

 * They are shown to be very good friends and are willing to do anything for each other.
 * Usually when boys try to hit on Jade, she'll just tell them to go away. And if that doesn't work, then Casper scares them.
 * Both go on misadventures.
 * Casper and Jade runaway from home together, only for the trio to find them and apologize for their behavior.

1995 version
See Casper and Jade McFadden

Casper and Jade McFadden is one of the central relationships in the Jade and Casper film.

Ghost and human siblings for over fifty years, Jade and Casper are close not in age but in friendship. They always have each other's backs. Jade will always see Casper clearly (both figuratively and literally). Casper, meanwhile will also see Jade that she is more than his sister, but his best friend.

They are sometimes called "Cade" or "Jaspe0.r"

Prequel universe
In the prequel universe, Casper and Jade are both twin siblings. However, Casper dies of a sudden illness and Jade is left alone after her parents' death and cannot be with him until they're both spirits.

Both of them meet again for the first time when Jade tries to escape the Trio and Casper passes her. They are both friends again by the end. Jade felt also hurt when Capser  hung out with their adopted uncles thinking he forgot about her. It took Casper a while to convince her he never forgot her.

Christmas version
They are more like best friends then siblings. Both of them work together to thwart the Ghostly Trio's plans, as well as scaring them in the process.

My Brother the Ghost versions
The two siblings were raised by their uncles, Stretch, Stinkie and Fatso Seymour. They are very close and was a miracle birth when their mother a ghost, had her husband's curse. However, Casper doesn't really mind Jade being human.