Human

A is a living being who resides in the Human World. Most beings who live in the Human World are Humans. A Human's body, like everything else in the Human World, is constructed out of and contains a Soul, bound to it by the Chain of Fate. Humans are the opposite of the Hollow.

Overview
The majority of Humans are completely oblivious to the dangers they are exposed to from Hollow and other evil spirits. It is unknown how many Hollow attacks against Humans occur under normal circumstances, but Hollows make their former loved ones into their first victims before they begin preying on Pluses and Humans with spiritual powers. A severe enough attack from a Hollow, or a Shinigami, on a living Human would not only result in bodily harm, but in the removal of the Human's Soul from the body. The damage can be easily repaired through Kidō if the Chain of Fate is not broken. Shinigami are forbidden by law from attacking Humans unless ordered to. They generally ignore Humans, but a part of their duties is protecting the Humans in jeopardy from Hollows. Some Shinigami have a tendency to view Humans as inferior, despite the majority of Souls, including most Shinigami, being of Human origins.

High-Spec Humans
A very small percentage of the Human population develops a high amount of Reiryoku; they are known as "High-Spec" Humans. These Humans can see and interact with Reishi-made objects, such as Souls, to varying degrees and for various reasons.

In even rarer cases, High-Spec Humans will develop powers, either spontaneously or due to an intervention, which will allow them not only to interact with Souls, but also to defend themselves and others against dangers posed by Hollows and other parasitic spirits.

Quincy
The Quincy are a group of Humans who learned how to manipulate Reishi and use it as a weapon for hunting Hollows. Due to a conflict with Soul Society and the Shinigami, the Quincy are all but extinct.

Fullbring
Fullbring is an ability which appears in Humans whose mothers were attacked by Hollows at some point. The attack left traces in the bodies of the mothers, which were later absorbed by the children while still in the womb. It enables its users to draw on the Souls within objects to make them do the user's bidding.

Trivia

 * According to Kūgo Ginjō, Fullbringers are the polar opposite of Substitute Shinigami.