Imprinting
It was even more difficult to train an Evil Spirit but it was not impossible.
All that it took was someone powerful to train it well enough to become like a hunting dog that only went after a designated target they had been given.
It was like directing a wild and savage animal toward a target, the training itself would not tame the nature of the animal and make it harmless but it would instead be harnessed in a way that it could direct that wild nature toward a direction they wanted.
The only way for a predator to be subdued was by force and that was where the ritual came in.
The black bandage Evil Spirit which was tied to Ash through the ritual would always feel like it was suppressed by an unknown force.
To the black bandage Evil Spirit, Ash was something that it could not go against that completely suppressed it.