Arcturus

An Arcturus refers to a Human with advanced physiology and superhuman capabilities. While not considered to be a threat outright, these beings hold power so great the entirety of Gotei 13 of Soul Society was tasked to personally oversee their existence and development.

Overview
The Soul King is an almighty entity tasked with the sole purpose of regulating the flow of Souls. While it is as absolute as a deity can be and considers perfection as the only acceptable standard, the work of simply one entity cannot be perfect for all eternity; often, the Soul King imbues one Human with the Souls of other supposed Humans, thus granting the aforementioned Human superhuman abilities and paranormal status. As the probability of said occurrence to happen is nigh impossible, but possible to some degree, the total number of all existing Arcturus at a time is rendered extremely low.

An Arcturus holds a plethora of powers and abilities that are considered supernatural to other Humans, and even exceeds the standards of the average Gotei 13 Shinigami if one is lucky enough. These powers and abilities vary and grow seemingly without limit; although each Arcturus must first acknowledge his/her status as one. Such powers may activate by extreme levels of stress at some point in an Arcturus' life, or may present itself during early stages of puberty. In some rare cases, perhaps even one in a million, an Arcturus may display such powers from within the womb of his/her mother.

Trivia

 * Arcturus is actually a giant red star present in the Northern Hemisphere of the Earth's sky. Source: Arcturus
 * I drew some ideas from the X-men's Mutants.