Lucy was startled by Alexander, but she repeated her concern:
"After all, Horror World can't mass-produce food. We can't survive like the ghosts of Horror World, who live off the endless Xiao fish from the depths of the earth. What will we do when we run out of food?"
"Right! Xiao fish! The endless Xiao fish!"
Xiao fish is a fascinating species, fundamental to the entire ecosystem of Horror World. Ghosts don't need conventional food and have seemingly endless lifespans. However, they do need to consume something, or more precisely, they require Ghost Energy to maintain their ghostly form.
There are many ways to acquire Ghost Energy, such as through ghost coins, by utilizing the fear value in Instances to absorb free-floating Ghost Energy, or various Ghost Treasures and places where Ghost Energy converges. But these resources are clearly out of reach for the most numerous and lowest-tier ghosts.