The unicorn is the purest of creatures.
As a steed only ridden by the lowest-ranking Cardinal Archbishops, it essentially represents the Holy Nation—some poets even use unicorns to symbolize the Holy Nation.
It requires at least a Fourth Level of Devotion Level, and one must carry the aura of the Pillar God. On top of that, one must be a pure maiden—even a Cardinal Archbishop who has mastered Advanced Divine Art, if male or a married female, would be rejected by the unicorn.
But Isabel is already pregnant, and in no way could she be considered a pure maiden; Aiwass is not even female, and the "Number 14" within him has already split and become Aleister. Theoretically, he shouldn't be able to touch a unicorn, or it would attack him.
However, during a previous wedding rehearsal, Aiwass inadvertently discovered this fact—he was still not rejected by the unicorn Pan Xi.
