From what I can tell, the Magic Cancel thing isn't a Royal Ostian trait. Asuna's membership in the royalty seems to be by adoption (thus making her Not-A-Blood-Aunt) given flashbacks that imply she's actually more closely related to the Lifemaker, though he uses "descendant", so it could be that the Ostian royalty are directly descended from the Lifemaker. No one else seems to have Asuna's magic cancel, however, as the only other example of it was the "depletion zone" under the ruins of Ostia where they intended to execute Arika, but that was due to the destruction of the Lifemaker's overwrite ritual.
---
"Oh, silver blade, forged in the depths of the beyond. Heed my summons and purge those who stand in my way. Lay
waste."
---
"Oh, silver blade, forged in the depths of the beyond. Heed my summons and purge those who stand in my way. Lay
waste."