The archetypal 'destructive mother' goddess of Yoruban myth, Oya was one of the wives of the storm-god Shango. With dominion over natural disaster, particularly in the form of hurricanes, lightning storms, and fire, Oya caused mass destruction-- but always in order to clear a path for new growth. In fact, it would be more accurate to call Oya a goddess of change-- or a catalyst-- than a goddess of disaster, for her storms and lightning are purifying forces which sweep away the stale and usher in the new. She represents sudden change, but her chaos is always necessary, and always precedes something better to come. Oya is also a symbol of feminine strength; this, along with the fact many mythological maternal figures are similarly known for "destruction or barrenness locked in a cycle with growth, birth, and bounty," (Demeter, Coatlicue) identifies her with the Empress Arcana.
This is the incarnation of Oya Nanami should have expressed, were she a whole individual. Instead, given her multitudinous issues, she has succumbed to Shadow Possession instead, and has been taken over by a version of Oya that expresses only the destructive components, and none of the creativity or benevolence that should follow Oya's purges. Blocked mid-cycle, Nanami wears a version of the goddess which destroys for no purpose, other than perhaps personal gratification, and which is blocked from the healing or guiding energies it might otherwise have expressed. For the sake of distinction one of Oya's other names, 'Yansa,' is used.