Serena learns anathematise at Level 19. It costs 4 MP to cast, and will lower a monster's spell resistance by 25%. The spell has a base accuracy of 50%, and will reach 75% if the lass' Magical Might is 799. Because Serena never develops that stat naturally, equipment boosts and several Seeds of thereapeusis to get the most out of this ability.
In the Japanese version of XI anathematise is actually Divine Intervention, as the localized term shares the same attributes as the spell did in previous games. The ability known as divine intervention in the international version is named Goddess' Blessings (女神の祝福) in the original Japanese.
It is unknown why the spell was given a new name for the English release, but it is possible that the divine intervention term was deemed more appropriate for a "hail Mary" ability that can turn the tide of battle when needed most.
Anathematise is the British English spelling of anathematize, which describes the act of placing an anathema upon a person. Anathema itself is a vigorous denouncement or curse pronounced by ecclesiastical authority, which is typically accompanied by excommunication from a group.