|“|| The Death Oath cannot be broken... Until one falls by the hand of the other... I accept.|
– War, accepting Uriel's duel of the Nex Sacramentum
Two beings vow to that one will kill the other. It is assumed that if this vow is broken there would be a dire consequence, as when War defeats Uriel he disobeys The Watcher saying that "The Nex Sacramentum is mine. I decide when the angel dies. Not you.". The Watcher then releases War from his magic, indicating that the Death Oath is a law he dare not disobey. It is unknown exactly what would happen if this law was broken.
Apparently the oath is contingent solely upon the death of one of the participants regardless of which one wins the initial fight. War defeated Uriel and claimed the Nex Sacramentum, but was latter killed himself by Uriel.
- In Latin, nex means "murder" or "violent death." Sacramentum means an oath (or a legal deposit or religious rite). The Latin meaning of the phrase "nex sacramentum" is unclear, since both words are nouns in the nominative case. "Death oath" would be expressed something like sacramentum necis.