Tales of Tolgard
Demi-god literally means half-god in Common. Traditionally, there are two major paths to achieving this state. One is automatic and the other must be pursued.
The first path is simply parentage. If you are born from the union of a mortal and a deity, than you will technically be a demi-god. However, in order to enjoy the full powers of this position, you will need worshipers.
The second path involves apotheosis. In this way a god or goddess grants you the status and powers of the position. This is most often a reward for the most faithful and successful followers of a deity.
A minor path, hinted at occasionally in arcane lore, involves complex ceremonies and many artifacts of great power. Still, when a mortal gathers sufficient power about themselves and followers the proper ceremonies, it is said that they can ascend to the divine. Whether or not this is true is a matter of heated debate among clergy and sages all over Materia.