From The Heretic Knowledge Vault
The Errant War ("Wars" in some readings) was a nasty civil war about two thousand years in the past that developed a year after the fall of Malacia and immediatly following the initial disappearance of Tsuiraku. According to Sarine, who delivered a lengthy monologue on the subject, the initial bone of contention was whether the elves should pre-emptively wipe out half elves believed to be "errants" or behave in a more restrained way.
As happens with wars, the original reason for fighting it eventually became lost, and bloodshed continued for its own sake, until the combatants stopped fighting out of sheer exhaustion. This precipitated the elven withdrawal from human society, which lasted until Veracia, in their misguided arrogance, broke the Elven shields with their poke-god Luminosita -- finally revealing Praenubilus Astu and the long-hidden Elves.
Sarine, who's older than she looks (to put it mildly), was around at the time of the Errant War. Although she's never admitted it directly, she was on the pro-half-elves side, which makes her anathema to some of the hardcore survivors like Yenhael. We learn late in the story that she was the recipient of an "Acts of War pardon" that restored her (more or less) to the good graces of the elves from a legal point of view, although it's far to say that a certain social opprobrium remains...