Her Omega Sister (ENGLOT girlxgirl)

In a world full of power and conspiracy, Elara Evergreen Brightburry, the Alpha heiress of the Brightburry Archduchy in the Veirtzoentia Empire, found herself consumed by an intense longing for her beloved adopted omega sister. As her younger sister returns to the family home after a decade-long absence, she finds herself desiring her even more than before. Now she finds herself caught in a dilemma, torn between fulfilling her role as a good sister and daring to venture into forbidden territory by declaring her sister as her one and only Omega.

This story set is in ABO World (Alpha Beta Omega)