Zenmetsu watched idly from the top of the roof, away from the battle.
From her contacts inside Seretei, there was a captain whom she agreed with. The one who also believed that there were only two types of battle: one to protect people, and one to protect honor. She couldn't remember the captain's name, but that was trivial.
She stayed out of the way for the singular reason that this was a conflicting battle. One man was fighting to protect, while the other was fighting for his honor. She very nearly grinned when she saw Ulquiorra grow enraged and change into his Segundo release. There wasn't a doubt in her mind that he would be victorious, but it was rare for her to see him in this state, so she stopped following the battle and concentrated on him. His lithe grace in battle demanded her attention.
More long minutes passed as he crushed the other into submission. Zen's eyes lit up as she saw the end of the battle begin. The other man was ragged and bloody, looking extremely desolate as if he had already given up. He hung, limp, his throat constricted by Ulquiorra's long tail. The boy was out of strength, out of options, and out of time.
Ulquiorra turned to address the woman that Aizen-sama had ordered be brought to Las Noches. She was the reason the boy was here and about to die, and he wanted her to know that. Ulquiorra's gaze flickered towards Zen for a moment, then back to the girl. "Watch closely. This is the moment the man you've put your hope in…" He started, placing the tip of his first finger on the boy's chest, over his heart. Zenmetsu glimpsed a flicker of black cero. "Will lose his life."
The girl snapped out of disbelief and screamed almost incoherently, but it was too late. There was a gaping hole in the boy's chest, his vital organs gone. Ulquiorra's tail uncurled from the boy's throat as he fell, lifeless, to the ground. The girl with the same oddly colored hair ran up to the boy and tried, futilely, to heal him. Even from here, Zen could see the tears that ran in rivulets down her cheeks. Orihime hugged his body tightly and wailed in absolute despair.
Ulquiorra turned to leave and sealed his Zanpaku-to, sheathing the blade. Zen cocked her head slightly at his approach. "Aren't you going to kill her? She's useless now. Far too broken to be of any use to Aizen-sama."
He shook his head, "Aizen-sama has not yet issued that order, and now she knows what extent we will go to if she disobeys. She is still useful." With that simple statement, he continued to walk away.
She watched until he was out of sight and then she too, shook her head. He was nothing if not obedient. Under normal circumstances, she would have followed, but this battle had worn him down.
It took a lot to anger him, and his second form was nothing but a powerful drain on his reiatsu. She would let him recuperate and she would take over the responsibility of watching Las Noches until he did so.
She cast her gaze in the direction of the girl who was still crying with all of her might, and decided to leave her alone. No more rescue parties would come for her, and the girl couldn't open portals to the other worlds, so Zenmetsu knew she didn't have to worry about the girl escaping. She opened her Pesquisa and, detecting no more foreign reiatsu, sat down and stared at the desert and crystal trees.
"I will show you true despair."
Zen imagined that, just maybe, he hadn't been speaking to the boy.