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The keys sound like a form of Restraining Bolt (might be a Slave Collar depending on how it's attached, since it's worn around the neck) that renders the wearer Incapable of Disobeying.
I was deciding against Hypno Trinket because, as forementioned, it's their bodies being controlled rather than their minds. Restraining Bolt seems to do it, but it's not a Slave Collar since it's merely hung on the neck by an enchanted (to be unbreakable) piece of string, so it's not clear they're enslaved. The protagonist was tricked into wearing one since it was offered as a gift. As a result the wearers are Incapable of Disobeying The Fagin.
Thank you both for the help tho :)
Pantheon Wick Cleaning
The antagonist has control over his pupils by having them wear keys around their necks which are actually enchanted so that they are physically incapable of disobeying him. When the villain uses it on the protagonist, it also has the ability of withholding the hero's magical powers.
It's not hypnosis in that the pupils are fully conscious of being controlled. In the hero's case, he even cries tears of rage as he's commanded to tear his beloved new tunic to shreds.