Becoming a Monarch Realm existence.
That was the last activation requirement and the one Alexia had almost fulfilled.
Luckily, she had discovered the curse and had chosen the fastest, most dangerous but most efficient way to prevent herself from fulfilling its activation condition.
Sadly, as the process of ascension had already been initiated, it was something that would now happen over time and Alexia would eventually become a monarch realm existence
Thus, if she did not remove the curse on her, it would eventually activate and Alexia would lose control of her body.
As for Roseborn's goal in casting such a curse, it was naturally so that he could use Alexia to give birth to his next vessel.
It was as simple as that.
The fact that he had placed the curse on her since she was just two years old signified that he was already ready for the possibility of her gaining a backer like Lucifer who would prevent him from getting to her on his own.