A Human (人間, Ningen) is a living being who appears in Bleach. Most characters who live in the Human World are Humans. A Human's body, like everything else in the Human World, is constructed out of Kishi (器子, Holdlets) and contains a Soul, bound to it by the Chain of Fate.
The majority of Humans are completely oblivious to the dangers they are exposed to from Hollows 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 Plus Souls. A severe enough attack from a Hollow, or - presumably - a Shinigami, on a living Human would not only result in bodily harm but also in the removal of the Human's Soul from the body. The damage can be easily repaired through Kidō if the Chain of Fate wasn't 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 fact that the majority of Souls, including most Shinigami, are of Human origins.
A very small percentage of the Human population develops a high amount of Reiryoku; they are known as "High-Spec" Humans. These Humans are able to 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.
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
Fullbringers are Humans whose mothers were at some point attacked by Hollows. The attack left traces in the bodies of the mothers that 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.