The Invisible Enemy! Hitsugaya's Merciless Decision

In flashback, the siblings Shōta and Yui Toyokawa wander Karakura Town as Souls after a fatal car crash, searching for their parents unseen by the living. One night Yui slips away, and Shōta finds her cornered by the Hollow that would become the Cloning Arrancar. Terrified, he flees and abandons her. In the present he confesses this guilt to Rangiku Matsumoto, who comforts him and points out that Yui was still saved and reunited with him.

Hitsugaya, meanwhile, is ambushed by an Arrancar clone disguised as a frightened Soul. He severs its arm, but it reverts to Soul form and vanishes, its Reiatsu undetectable. Comparing notes back at Orihime's apartment, Rangiku suggests Yui may have been the very first Soul the clone encountered. Watching the girl, Hitsugaya realizes the clones can pose as Human Souls to hide and multiply, and fears Yui herself may be one. His attempt to perform Konsō on her fails, confirming the Arrancar tampered with her, so he seals her inside a Kyōmon barrier and sends her Reiatsu to Soul Society for analysis.

The next day, Yui coaxes Shōta into pressing his hand against the barrier alongside hers, and his matching Reiryoku dissolves it. Akon reports the grim results: Yui is a clone created by the Cloning Arrancar, controlled by it, and destined to vanish when it dies, while Shōta is the real target for his strong Reiryoku. Yui leads Shōta to the park where Ulquiorra once landed, then erupts with red Reiatsu as Arrancar clones swarm. An eerie melody drags Shōta toward her against his will while Rangiku cuts down the clones. At the last moment Yui's blue eyes return, and she screams at Shōta to stay away, briefly wrenching back control of her own body.

The Cloning Arrancar's power to disguise itself as a Human Soul is revealed, along with its history of first devouring Yui's Reiryoku. Hitsugaya seals Yui in a Kyōmon barrier, which Shōta unwittingly helps her break using his own Reiryoku. Analysis confirms Yui is a clone that will disappear if the Cloning Arrancar is destroyed, and the Arrancar targets Shōta, luring both children into a swarm of clones in the park.

Listed among the anime-only episodes, this installment sits within the Arrancar arc and adapts no manga chapters. Its opening is Alones and its ending Tsumasaki. An "Arrancar Encyclopedia" segment has Gin begin to explain the Arrancar numbering system, only for Ulquiorra to stop him before his own number is disclosed.