The relationship between the two sisters was convoluted from the start.
Their birth was not a mistake.
In reality, the Divine Emperor had a plan in conceiving them.
His relationship with the Nox had completely broken down by the time he made it to Apeiron. Because he didn't want to be their slave, he used the universe as a safehouse to get away from them and build a life for himself.
Unfortunately, they found him early and he wasn't able to establish the foundation he wished for, but he was able to leave two contingencies for revenge.
They were named Zara and Alwa.
Originally, they were supposed to be born at the same time, and at a point where his existence wouldn't be unknown to them.
He hoped to create a chance to strike the Nox through them, giving Nox lineage to universal denizens and giving them a chance to conquer the very power that oppressed them.
However, life was not kind to him.