Many of Bleach's villains are simply beyond redemption because all they want is power, often at the expense of others. Captain Sosuke Aizen stole the research of Kisuke Urahara and hatched a grand plan to assume the throne of heaven, and he created the unmasked Arrancars to aid him. But one Arrancar was different: Nelliel Tu Odelschwank.
Nelliel was among an earlier generation of her kind before Ichigo fought Ulquiorra and Grimmjow in the main story. From the very start, Nelliel had a good heart, promising to represent a change for the better among her kind. Sadly, betrayal cut that idea short.
A Reason To Fight
Nelliel was once a powerful Menos Grande and became an Arrancar. She granted the rank of #3 among the powerful Espadas, Aizen's top minions. The Espadas were a gang of bloodthirsty, self-centered thugs, but Nelliel was different: she never fought in the battle for its own sake, instead of fighting for clear purposes such as protecting her dear fracciones or simply to defend herself. To her, battle was not a path to glory or honor; it was a bloody tool used to shield the innocent from harm. Although Nelliel was among the strongest Arrancars of her time, her attitude made her a target, and Nnoitora and Szayelaporro Grantz despised her.
Nnoitora Gilga in particular sought power above all else; he could only prove his worth by taking on, and defeating the strongest of foes. His personal goal was not unlike that of Grimmjow, and it made him Nelliel's total opposite. Nelliel's compassionate nature stood out clearly next to Nnoitora's selfish and thuggish ways, leading to a feud that culminated in Nelliel's expulsion from the Espadas entirely. Nelliel refused to misuse her strength to bully the weak or seek shallow validation from winning battles. If she got her way, she'd never had to draw her zanpakuto again, but she drew it every time Nnoitora challenged her.
Nnoitora eventually teamed up with Szayelaporro Grantz to take Nelliel out of the picture once and for all. They distracted her with an explosive that injured her fracciones, then Nnoitora ambushed her and wounded her head with his blade. Nelliel's spiritual pressure leaked from her wound and Nnoitora tossed her weakened body off of Las Noches' palace roof and into the Hueco Mundo desert. Nelliel's compassionate ways had failed her... for now.
Her True Strength
Nelliel returned as Nel, a toddler with no memory of her past life. She met Ichigo, Uryu and the others when they invaded Hueco Mundo, and she was present as Ichigo fought the Espadas. When Ichigo was cornered by Nnoitora, Nel was distraught and her full power returned, along with her adult form and memories. Once again, Nelliel was fighting for the sake of others, not herself, and that demonstrated clear strength of character as well as body. Nnoitora's constant pursuit of power was futile, but Nelliel's compassion and mercy protected the lives of other people and helped create a better world.
Nelliel risked her life to keep Ichigo safe and repay him for protecting her up until this point. The only reason she failed to finish the fight against Nnoitora was that her temporary adult form wore out. Until then, however, Nelliel proved that even among the Arrancars in the cruel world of Hueco Mundo, compassion and faith in others always trumped selfish ambition and treachery.