Description
That oculon is what binds the Yrlwalach to Crucia's will. If you can destroy that dread artifact, then her control over that beast will be removed. I've consulted with Finric Rhen, and she is in agreement with this analysis. I believe her words were, "Better an uncontrollable Akvan horror, than one at the bidding of a bird dragon in a naked mammal's body." My liege knows how to turn a phrase.
They're preparing a ritual upon the Altar of Storms. If their control of the Yrlwalach isn't yet complete than the oculon will be there for you to destroy. And if their control is complete, then it won't matter anymore.
Upon completion
You did it, [%NAME]! You broke the Storm Queen's control of the Yrlwalach!
The Akvan are dangerous enough on their own, but they get distracted plotting against each other as well as with higher level mathematics and cooking. The Rhen wasn't exactly clear.
If Crucia had focused all that thing's power upon us, not even you would have survived. But we stopped it! We defeated Crucia! Now we just have to worry about the thousands of contingency plans I know she has working in the background.