Rex Signum

Rex Signum (宝具の原王 (レックス・シグナム), Rekkusu Shigunamu; Latin for "King's Symbol" and Japanese for "Precious Tools of the Original Kings") are ethereal weapons uniquely located within the, and a select few being even further hidden away in the Soul Society West Branch. The weapons are similar to, yet distinct, from Zanpakutō, being spiritual weapons which house souls and grant abilities to those who wield them — the similarities, however, stop here, as the Rex Signum branch off into their own distinct line from this point forward.

Attributes
The Rex Signum are items, almost exclusively weaponry, without any unique abilities unto themselves. They are, however, quasi-sentient instruments, and while they cannot communicate with their wielder, a Rex Signum always chooses someone who fits its properties. This is due to the fact that a Rex Signum is an item bequeathed with a portion of the soul of a former monarch — a king, queen, or other some such sovereign — who has ruled over what is now known as the United Kingdom of Great Britain and Northern Ireland. This soul fragment only responds to a soul of a similar strength of will, thus the weapon or instrument that the soul resides in will respond to that person and that person only from the moment it is claimed until the moment the wielder passes. Despite the Rex Signum not having any unique abilities, they do each possess a single, solitary strength: Power Enhancement and Cultivation.

Whether or not an individual realises it, all Humans are born with the ability to develop unique strengths. Those who do are referred to as Psysis (魂の (プシシズ), Saishizu; originating from the Greek, ti̱s psychí̱s, meaning "of the soul, spiritual"), or otherwise "High-Spec Humans". Whatever the term used, the result is the same. Psysis are humans who have developed a supernatural ability — be it as simple as spiritual awareness, or a more complex ability like those displayed in Fullbringers — and where the Rex Signum displays its strength is the fact that it can trigger, cultivate, and draw out the abilities of Humans. The principle is seemingly the same as the one used by the Quincy,. The soul within the instrument, the Rex Signum, responds to the similar soul that it has chosen; two souls do what one could not, and strength within the wielder bubbles forth, resulting in the awakening of their hidden talents. The end result is always different for each Rex Signum wielder, and as such, no two wielders of the same Rex Signum in history have ever had an ability that are completely the same.

Rex Signum are not limited to simply Humans; Souls are capable of wielding them as well, and this extends to Souls such as, should they be so chosen. In the case of a Shinigami wielder being chosen by a Rex Signum, the ability they develop will be separate and distinct from that of their Zanpakutō, though superficial similarities may remain. For any other Soul, the result would be the same as if a Human was chosen.

Arrancar and Hollows, however, are rejected by the Rex Signum, and cannot be chosen as wielders. This is due to the fact that the Rex Signum themselves are particularly lethal to Hollows, purifying them in the manner akin to a Zanpakutō.

The amount of Rex Signum within the United Kingdom and the Soul Society West Branch have not been properly documented, but are said to number in the same amount as the monarchs themselves.