Rayearth (OVA): Princess Emeraude

She's the former Pillar of Cephiro, she was once a noblewoman of her world, and had later used her power as the Pillar to prevent her younger brother, Ferio from being punished for stealing something from her but in her manga counterpart, there is no mention of Ferio stealing something from her, and he does remember that she is his sister; in fact, he left the palace on his own will. Once the Magic Knights fought and defeated Zagato, the high priest of Cephiro, she was thrown into despair from loss and grief over her loved one's death, transformed into an evil version of herself and fought the Magic Knights after being freed from her water prison. The Magic Knights had no choice but to accept her last wish: by killing her in order to be with Zagato.