The Esper Saga
Half-Espers are children of the gods. They are those individuals who have one human parent and one Esper parent; since some of them have Esper mothers, evidently the Espers can give birth while bearing human form. Half-Espers are hard to categorize, being as varied in abilities as their parents, if not more so – for many Half-Espers develop secondary powers not possessed by either of their parents.
Half-Espers have existed for a very long time; indeed, Diablos was imprisoned for killing Half-Esper children.
Generally, all half-Espers can manipulate Magi, and most of them can perceive it. Beyond that, though, their abilities are strange and unpredictable, though they seem to follow a general theme of elemental manipulation. Exceptions exist, though.