From the introduction:
In this world, both ghosts and witches exist. The year is 1997, and the titular Casper has only just become a ghost. Should events proceed as normal, over the next few days he will make his very first friend, form a family with the Ghostly Trio, and dub himself ‘The Friendly Ghost’. About a year later, Casper will go on vacation with the Ghostly Trio. It is then that he will meet Wendy, a witch, and form a friendship with her as well.