Mind control sex stories, are those where mind control and even telepathy, is somehow used as part of a sexual act.
One of the most commonly used mind control techniques is hypnotizing someone, and then using suggestions to make them perform sexual acts or bring themselves to orgasm while under hypnosis. Characters are often hypnotised into behaving less restrained than they might be in real life.
A person may have a secret longing to be used as a sexual plaything, but are unlikely to realise that fantasy unless it was brought out under hypnosis. Another common theme in mind control stories, is turning the hypnotised person into a "people puppet", where the "villain" may use his psychic powers, to manipulate the limbs of his "victim", as if they were a puppet. For example, a person may not wish to be servile to another, but might be forced to kneel down in front of them (and perform various "services"), in a case of mind over matter.