HEADCANON: Aspect of Death
An arrancar’s aspect of death is a very personal attribute, possibly reflective of their personality or mortal death. Therefore, I don’t believe that just because two Espdada share the same rank, they necessarily have to share the same aspect of death. Looking at Nelliel’s behavior, I believe hers to be Justice.
Her hollowfication stemmed from a death in which she was wrongly persecuted for her religious beliefs, and executed in a crusade. In her last moments she raged against the injustice of it. Nelliel proceeded to hollowfy fairly quickly, and sought out the ones who caused her death, thinking herself to be righting the wrongs committed against her in life.
As an adjucha, this led her to largely abstain from consuming her fellow hollow unless they challenged her directly. It was fair, in her way of thinking, when they were the ones to instigate it. And as her power increased, she had no lack of them, lured by her ever growing strength.
When she was first approached by Aizen she was distrustful, but at the same time, she found herself drawn to his aura of authority. He had the potential to bring order to Hueco Mundo, to lift them from the chaos of scraping along the endless dunes. And more importantly, it gave them an opportunity to stand up to the Shinigami in a way they’d never done before.
Nelliel rarely ventured out of Hueco Mundo, but she knew lesser hollow in particular were drawn to the world of the living like moths to a flame over the prospect of fresh souls. There they were slaughtered by the Shinigami, when they were simply acting on their nature, never knowing any better. She considered it a great injustice that so few of them were able to evolve to their full capacity and regain the reason that allowed them to choose, and to live as something other than beasts. Under Aizen, she saw a future where every hollow would regain this capacity, and so she allowed herself to become an arrancar.
As an Espada, we see her behave rather self-righteously at times, particularly in her interactions with Nnoitra. She believes her own moral code to be the epitome of what is right, and what is wrong, and she is more than willing to enforce it upon others.
“There was a time where we ceased to be human and became beasts. And then in becoming arrancar, we regained our capacity for reason. One who posses reason,should require a reason to fight.”
Her most prolific quote also reflects her need to have a cause, something she considers right, worthy, and just to raise her blade. And we see she is more than willing to enact retribution should a crime be committed against her, or those she cares about, again in the case with Nnoitra and his attack against her fraccion.
On a more meta level it also goes well with her design and resurreccion. She is a Knight in Shining Armor, so to speak. It calls back to chivalry and the virtues of honor and bravery. It could even be argued her release command, “Declare”, could be likened to someone passing judgement, ringing with finality and marking them for sentencing.
Such a strong, inner sense of justice leaves Nelliel with the potential to be quite hypocritical and fall into a black and white thinking where she considers herself judge, jury, and executioner. It also leaves her extremely judgmental. We see her voice her thoughts and opinions as though they are fact many times, and in her mind, they are. Ultimately it is where many of her flaws are born, but also many of her strengths, such as her loyalty, her compassion, and her protectiveness – which is why I believe it’s a very fitting aspect and goes a long way in explaining her character.