A stealer of hearts is a type of fae of utmost danger to mortal kinds. The stealer of hearts may seem innocuous at first, appearing only to desire a mortal's willing romance; indeed, faer desire for untainted love means these fae will generally avoid underhanded methodology in faer courtship, instead employing faer best approximation of mortal courtship rituals.
The danger of the stealer of hearts is in fact related to this adherence. For a creature of unbounded life and unbounded love, the clause "till death do us part" presents a disastrous possibility. A common solution to this is to trap faer lover's soul inside a gemstone, where it can be admired from the outside for all eternity.
Thus if a mortal is approached by a fae adorned in lustrous gems, whose courtship recalls that of their parents' time, they are strongly advised to turn down their suitor, lest they become the latest addition to the stealer of hearts' collection.