The Invisible Enemy! Hitsugaya's Merciless Decision

The arrancar is revealed to be able to disguise itself as the human souls it has devoured. Upon learning of the attack on Yui by the arrancar, Hitsugaya assumes she is one of the copies, and his inability to send her to the Soul Society confirms this. Still unsure, Hitsugaya has the Soul Society track the disguised arrancar while Yui is sealed within a barrier. The analysis confirms Yui is one of the clones, and that the arrancar acquired its cloning power from her. As Yui's brother, Shouta has similar powers, and Yui uses him to break the barrier.