The 4th Espada in Bleach, assumed to be the fourth most powerful of his ilk, is Ulquiorra Cifer, whose deathly aspect is shaped by abstract concept of Emptiness. In other words, he claims to have no feelings or emotions about anyone or anything (even though he's clearly loyal to Aizen.)
His body does bear signs of the truth, however, considering that his Hollow hole is positioned where his heart is meant to be. Is everything about this mysterious Espada known, though? Or does Ulquiorra have secrets that he reveals to none but himself?
10 His True Strength Is Healing
More than anything else, Ulquiorra's real power is his healing ability, with which he is able to "regenerate" damaged body parts in a short time (often before the enemy has even realized what's happening.)
For instance, when Vasto Lorde Ichigo tears his arm out of its socket, Ulquiorra easily rebuilds it and is ready for his next move almost immediately. However, he states that this does not apply to certain constituents of his anatomy, such as his internal organs.
9 He Can Communicate His Experiences
In line with the previous technique, Ulquiorra possesses a rare power known as Solita Vista — here, he extracts one of his eyeballs, crumbles it into sparkly dust, which then moves towards his targets.
Apparently, this powder translates Ulquiorra's experiences, perceptions, as well as emotions (not that there are a lot of those, to be honest.) Luckily, his reconstructive properties allow him to grow his eye back without any sign of injury or side-effect.
8 Ulquiorra's Changing Appearance
When Ulquiorra is brought into play, he looks rather macabre, what with the black hair, green eyes, and teardrop lines extending along his face. He is explicitly inexpressive, opting to retain his deepest secrets without revealing them to anyone, even the Aizen-sama he worships.
Interestingly, his Hollow hole is first depicted on his neck, but the location changes later to the breastbone (in order to reflect his relationship with the human heart and its so-called "love" that he blindly despises.
7 Ulquiorra Tortures Himself
Ulquiorra is rare among his kind for actually remembering his time spent as a Hollow (probably a Vasto Lorde, although unconfirmed.) Nevertheless, he was not one to seek the glory of power, regardless of his strength, but rather ruminated on his existence and its meaning for the most part.
As he traversed the empty wastelands of his home, he finds a dead tree decorated with several sharp protrusions. Ulquiorra believed that he might experience at least some kind of feeling by crucifying himself on the branches, but even this doesn't give him the solace he desperately needs.
6 Double Resurreccion
Ulquiorra's zanpakuto, Murciélago, expands into a magnificent form: a human-bat hybrid with vastly increased reiatsu. While released, he is overwhelming, throwing Ichigo around like a rag doll and basically "punishing" the kid to satisfy his own sense of sadism.
Unlike the other Espada, Ulquiorra can trigger his Resurreccion for a second time, giving rise to the Segunda Etapa. At this point, he becomes nearly unstoppable, and his spiritual pressure alone is said to induce asphyxiation even in powerful opponents.
5 Limitless Green Spears
In the Segunda Etapa stage, Ulquiorra generates a renovated version of his potent spears of green light, known as Lanza del Relámpago.
This weapon is ridiculously destructive, considering that the explosion it produces is so enormous that the massive fortress of Las Noches looks like a toy house next to it. That's not all: Ulquiorra announces that he can unleash a barrage of these lances, although Vasto Lorde Ichigo destroys his second attempt with his bare hands.
4 His Speed Is Unmatched
One of Ichigo's foremost features his is spectacular speed during combat; he proves his aptitude for shunpo when he dodges every single petal of Byakuya Kuchiki's bankai, Senbonzakura Kageyoshi.
However, Ulquiorra's sonído, even against his terrifying new adversary, is nothing to be scoffed at. In fact, Ichigo is barely able to comprehend the Espada's motions when they first fight each other. Even more impressive is the fact that Ulquiorra could employ sonído after losing one of his legs.
3 The Cero Oscuras
Ulquiorra, like many high-level Arrancar, is able to create a Cero, a Hollow energy blast, but his version is far more extreme. A single Cero Oscuras (also known as "Black Hollow Flash"), is capable of tearing an enormous hole in the roof of Las Noches, an unimaginable feat by itself.
The resultant outburst simultaneously rips the Hollow mask off Ichigo's face as well. No wonder Aizen specifically forbade the first four Espadas from activating their Resurreccion within the dome.
2 His Fights Are Less Gory In The Manga
Once Ichigo is "reincarnated" into his Vasto Lorde form, Ulquiorra is forced into defensive mode (because he doesn't have any other choice, really.)
At one point, Ichigo severs his right arm, which is depicted in the anime; but while the manga shows him flinging it at Ulquiorra, the anime changes the object into a gigantic block of granite. This alteration doesn't make a lot of sense, because the actual act of dismembering is shown in quite a brutal fashion.
1 He Has Always Had A Heart
Before his eternal disintegration, Ulquiorra confesses that he finally finds human beings and their emotions a fascinating topic for study. He inquires if Orihime still remains fearful of him, but she responds in the negative (taking pity on the dying Espada.)
Ulquiorra then realizes that a heart is not simply an organ located in the body, nor anything tangible, for that matter. Instead, it is a term used to describe the bond between people, a metaphor that he grasps a little too late.