Here's a theoretical possibility of tarusta using the chaos emeralds. Part of her colors reference the synchro summon mechanic of duel monsters (one of the rings, in her case the ring of a non-tuner monster). If you look close enough, her necklace went from being a star rating of a monster card to the color of one of the orbs used for synchro summoning. She may sometimes achieve this form when she's initiating a synchro summon.