Jujutsu Kaisen is a series filled with incredible concepts and ideas that are all held together by a complex and layered system of rules that revolve around Jujutsu sorcery. These rules govern the way that the world has worked for centuries and contain many interlocking parts that can either work for the benefit or the detriment of Jujutsu sorcerers. Both Cursed Spirits and Shikigami fall under these preexisting rules.