There are three classes in omegaverse; starting from highest Alpha ,next beta, and lowest an omega. Omega males were the rarest out of all of them and are prized possessions to some alphas. Asta was born an omega, while Yuno was born as an alpha. Never did asta think he would have to submit to an alpha, but he can no longer ignore the feelings welling inside of him. Nor the constant pestering of the black bulls. - #1 on astaxyuno