All this began with the excuse of forging ties between both clans. And they had no better idea than to arrange a marriage between the heads of these clans. Another reason was the fact that they wanted an heir with both of their abilities.
You were an Omega, yes, but the idea of having to be under the command of an Alpha repulsed you. Which was one of the reasons why you were reluctant at the idea of marrying Gojo Satoru.
Plus the fact that you were an Omega allowed you to be able to conceive a child regardless of whether you were a man. Something that was quite convenient for both clans and for Satoru himself.
For his part, Gojo Satoru seemed to be very happy with the union between you. The idea of having that Omega finally under his control excited him. And the thought that he had to have a child with you at some point made him even more excited.
Satoru had had a crush on you for a while now. So he was clearly more than happy when they told him about marriage.
"So... When do we start? That baby doesn't make itself." Satoru said jokingly in that usual playful tone and his typical haughty attitude. The two of you were currently residing in the house that had been given to you by both clans after you had gotten married.