Many heroes and villains populate Bleach and after the Soul Society arc is concluded and Rukia is saved from execution, a new enemy arrives. Just as Ichigo makes peace with the Soul Society, Byakuya Kuchiki in particular, Sosuke Aizen unleashes his Arrancar army on the world, and that includes the 10 mighty Espadas. But there's a fallen Espada who really stands out from the rest: Nelliel.
On a personal level, Nelliel is unusual in that she is not a bloodthirsty thug, nor is she fanatical about Aizen's supposed role in saving Hollow-kind from their cursed existence. In fact, Nelliel made friends with Ichigo when he arrived in Hueco Mundo's desert, and she quickly proved to be an odd but lovable Arrancar with more than a few secrets.
Nelliel Has Two Forms, Not Counting Resurrection
All Arrancar can transform their bodies when they release their zanpakuto, such as when Grimmjow becomes a panther Hollow upon releasing Pantera. But Nelliel can transform even without the use of her zanpakuto (Gamuza). Some time ago, her bitter rival Nnoitra Gilga conspired with Szayelaporro Granz to strike Nelliel down, and Nnoitora struck a serious blow on Nelliel's head.
Spirit energy bled from the injury, and incredibly, Nelliel shrank into a toddler, and her Hollow mask remains changed to suit her new look. Later on, when Ichigo was cornered by Nnoitra inside Las Noches, Nelliel transformed back into her adult form in a moment of distress, and her mask changed back, too. No other Arrancar has been seen doing anything like this, and not even Szayelaporro is 100 percent of how this works.
Nelliel, Surprisingly, Can Deflect Ceros
Arrancars, like Hollows, can charge up their spirit energy and fire it in a destructive cone, an ability called cero. Nelliel is the only Arrancar who can actually deflect them, and she does it with her mouth. In child form, she can open her mouth wide and absorb a cero blast, twist it around, then fire it back at the enemy, with no loss in its destructive force. She once did this to Dordoni to protect Ichigo, much to everyone's surprise.
Meanwhile, in adult form, Nelliel can absorb the enemy's cero in this manner, then fire it back with her own cero, creating a double blast called the Cero Doble technique. Nnoitora has seen this technique used before, but that won't help him survive it unscathed.
Nelliel's Mask (and Teeth) Changes Often
When an Arrancar releases his or her zanpakuto, their Hollow mask remains will change and probably get bigger. Nelliel's mask remains, which sit atop her head like a hat, change often. Originally, she had a mask with upper teeth, two horns and eye sockets, but when Nnoitora struck her, Nelliel's mask was damaged. The mask lost all its teeth on the left side, and a crack was put onto the remains. Then, when Nelliel shrank into a child, her mask became simple and cartoony, still missing its left teeth.
Later still, Nelliel transformed back and had her adult mask back, with the left teeth still missing. Finally, she released her zanpakuto, and her mask remains became a slightly different version of their regular form, but the left teeth were still missing. The only constant here is that when Nelliel lost her mask's left-side teeth, those teeth were lost forever.
Nelliel's Healing Powers Are Pretty Gross
Arrancars don't typically have healing powers, but Nelliel does have negligible healing abilities, even in her child form. Nelliel claims that when she drools on someone, her saliva will heal minor wounds, and she even did this to Dordoni when Ichigo defeated him, as a gesture of goodwill. Dordoni wasn't impressed, though, and he was downright disgusted when Nelliel took the next step.
Nelliel, who was clearly having too much fun, wiggled her own uvula and set off her gag reflex, vomiting clear liquid all over Dordoni in an attempt to heal him some more. Nelliel claimed that this was also healing saliva, but Dordoni recognized it for what it really was, and he was not happy. Just how much saliva/vomit Nelliel can offer for a wounded patient is not quite clear.
Nelliel's Memories Only Go One Way
Nelliel's memories are rather disorienting at times. She remembers different things in her child and adult forms, and the memories don't always cross over. In her child form, Nelliel cannot remember anything that happened to her during her adult days, meaning she had no idea that she had once been Espada #3 -- and she didn't believe Nnoitora when he announced this. However, when Nelliel regained her adult form, she remembered everything, including her original Espada days and the time she spent as a child.
Nelliel clearly recalled her time with Ichigo up to this point, and she wanted to repay him for all he'd done for her so far. Once Nelliel's adult form wore off and she became a child again, she couldn't remember what had just happened during her fight with Nnoitora in her adult form. Clearly, her adult body has a much stronger memory retention ability than the child form. Then again, her child self might be traumatized if she recalled all the violence and bloodshed of her adult days.
