With every advancement, Ulquiorra's recovery abilities underwent a qualitative improvement.
As a small Hollow, he had ordinary recovery. As a mid-sized Hollow, it advanced into advanced recovery.
When Ulquiorra became a Gillian-class Menos, advanced recovery evolved into regeneration.
Regeneration was no longer a low-level ability comparable to mere "recovery," but a powerful ability capable of regrowing severed limbs.
As long as he did not die immediately, he would fully recover after resting for a while.
As an Adjuchas, regeneration evolved into rapid regeneration.
As a Vastolorde, it evolved further into high-speed regeneration.
Then, after Ulquiorra became an Arrancar with the aid of Aizen Sosuke's Hogyoku, his high-speed regeneration evolved into "Super Regeneration."
Under the effects of this ability, as long as Ulquiorra was not struck in the head and killed in a single blow, and possessed sufficient spiritual pressure, no matter how severe his injuries were, he would recover instantly.
That sneak attack just now only cost Ulquiorra a bit of spiritual pressure to heal. It did not even count as an injury.
However, when Lord Aizen assigned him the task of guarding the Hogyoku, he had also told him that if anyone came to steal it, he was not to stop them. He only needed to let them take the Hogyoku away.
Those two three-digit Arrancar had no idea that even if they had not ambushed Ulquiorra, once the battle began, Ulquiorra would have held back and allowed the two of them to take the Hogyoku.
And that slash had given Ulquiorra the perfect reason to let them go.
Although Ulquiorra did not understand why Lord Aizen had made such arrangements, he only needed to obey Lord Aizen's orders.
As for everything else, Lord Aizen had his own plans.
The three Arrancar figures leaped from one massive pillar