Royal Hollows

A Royal Hollow (or sometimes shortened to just Royal) is a Hollow (Probably a Menos) who has acquired Shinigami powers, making it much like the exakt opposite of a Visored, even more so than Arrancars. The only known Royal Hollow is Kuro.

Functioning:
It is mostly unknown how Kuro evolved into a Royal Hollow, but it is known that he was turned into one by other Hollows, along with some other victims that did not survive the experiments. However, the Hollows that experimented on him did not realize that stepping into the Shinigami's territory could cause betrayal and/or too great power. Following this mistake, Kuro fled Hueco Mundo.

Appearance:
The appearance of a Royal Hollow is much like that of a regular human, but can enter a state where the Royal Hollow forcifully drags him/herself closer to both Shinigami and Hollow, turning him/her into a Hollow-like form. This power is called Evolución.

Abilities:
A Royal Hollow can use the Cero and functions much like a Hollow, but with much greater power. Strangely enough, they do not seem to have any abilities of the Shinigami, i.e the Zanpakuto and Kido, but presents an entirely new ability known as Evolución.

Evolución
The Evolución (Spanish for Evolution) is the primary ability of the Royal Hollows. It consists of a certain part of  the Royal Hollows body that is transformed into a white, marble-like part. This certain part itself has some abilities itself, but mainly serves as the "Key" or "Lock" for the Evolución (Much like the Zanpakuto is a "lock" for the Arrancar, and the sealed state of the Shinigami's Zanpakuto is the "lock" for the Shikai). The Evolución of a Royal Hollow is much like the released form of the Arrancar, or the mask of the Visored (although the Evolución transform/covers most of the Royal's body). While in this state, the Royal's overall battle skills improve, and they also gain some new abilities.