A necromancer must either find unburied dead in mass numbers after a battle or famine, or cause a battle or famine, to gather the bones left thereafter. They must then clean and arrange the bones, making sure there are enough of each kind to form the shape and size they want, then spill their own blood into the mouths of each skull. This ritual (28) will create a gashadokuro if repeated for three nights.

To control a gashadokuro, one must steal thirteen skulls from the giant and crush them into powder, then drink it mixed with spoiled milk. To summon one, one must leave a circle of powdered skull large enough to hold the gashadokuro around a pool of blood, then speak the names of thirteen dead that are part of the giant. To capture and draw power from a gashadokuro, one must bind it with a rope of flesh.