The magical effect that Buya exerts on the victim, draining magical juices, has gained great strength due to the fact that the victim is under the influence of Chuudnogo Dary of a benevolent demon #ARTIFACT[2854, Chuuji].
As a result, the victim pays with their own health for using magic, equal to 15% of their magical damage. Getting rid of this magic and preventing its reapplication can be achieved with Rejection Curse, owned by Demonologists.