A wounded deity comes to realize the limits of his power in the heartbreaking second installment of the cycle on the San Francisco Opera (Saturday, 1 pm). Wotan, king of the gods, strives to undo the curse of the ring by fathering a pure-of-heart hero by a mortal woman. But he finds himself torn as events spin out of control and his offspring defy his will. Wotan’s deeply loving but disobedient daughter is sung by soprano Nina Stemme, who makes her cycle debut.