Fire's Watch

The Guardians of Hestia are people that can be human, demigod, or nymph. Each guardian has sworn loyalty to the goddess Hestia, to join and follow her. Like the Hunters of Artemis, they're made immortal by Hestia and given new powers by her, as long as they do not break their oath.

Description
The Guardians of Hestia are gifted with excellent combat capabilities and the power to control fire, possess eternal youth as long as they do not die in battle or break their oaths, and can use limited medicinal powers. They can't kill anything - even monsters - unless it is absolutely needed. They are considered as family by Hestia, and as such are all brothers and sisters. They are however sworn to be guardians forever and to be eternal peacekeepers. Because of this, they disgust very much senseless fights and violence of any kind.

If a guardian breaks the oath, Hestia will remove their gifts and banish them, taking all of their memories about the guardians away. The other possible way to lose immortality is to die in battle.