In the various works of Hajime Kanzaka, humans make up a large number of the principle and supporting characters. For the most part, they are the same as or similar to humans of the real world. However, in some of his works there are important differences; this article will focus on those differences.
In Slayers, humans exist on two planes, or sides, simultaneously. The mind, or spirit, exists on the astral side (or plane), while the physical body exists on the physical side. Because of this, humans are vulnerable to attacks from both the physical and astral sides. This makes them different from mazoku, who are only vulnerable to astral attacks since they are entirely astral beings with an artificially created physical body.
If a human is attacked on the astral side (for example by an astral spell like Elmekia Lance), it will cause damage to their mental abilities. Depending on the strength of the attack, it could limit their ability to focus, paralyze them, or even put them in a coma. A very powerful astral spell, like Ra Tilt, would most likely destroy a human's astral body, effectively rendering them brain-dead.
Furthermore, many humans also have the ability to use magic, though this varies from person to person and from place to place. Humans use magic by calling on magical power from another source, usually from the astral side (called Shamanistic and White magic), from a mazoku (called Black magic), or, less commonly, a shinzoku (called Holy magic). It is also possible for a human to summon power from the Lord of Nightmares (Ragna Blade and Giga Slave), though the only person known to do this is Lina Inverse.
A human's bucket capacity determines how much magical power they can use at one time. A greater bucket capacity means that they can use more powerful spells or multiple weaker spells at once. Though bucket capacity is fixed at birth, it can be amplified through means such as using the Demon's Blood Talismans. Pool capacity determines how much magic a human can use before becoming exhausted. This capacity can be increased by increasing stamina.
Most if not all humans are born with at least the bucket capacity to use Lighting, the weakest spell in Slayers. Power beyond that varies a good deal for reasons not entirely understood, although it is implied that the people capable of more powerful magic are a minority. When the mazoku barrier was created during the Kōma War, the humans living within it and outside were completely isolated; the former group became well-versed in practicing magic, while the latter developed more advanced technology utilizing inventions such as gunpowder. Whether the absence of magical knowledge of the humans outside the barrier is caused by the lack of magical tradition or a generally lower typical bucket capacity is a subject of debate. After the barrier was destroyed in 1012 AK(?), these differences already began to fade.
Humans inside the barrier were able to use shamanistic, white, and black magic; however, because the barrier cut them off from the power of the shinzoku, they lost the ability to use holy magic. Since the barrier was destroyed, however, it is possible that they have regained this ability, though this is not explicitly stated in canon.
Humans living around the area of the barrier are mostly from the europid and/or mongoloid races (the art style used makes it hard to determine), but according to Kanzaka, negroid people can also be found in more distant lands. All humans seem to share a single language within the barrier, with some minor variations depending on the locale.  How the language(s) spoken outside the barrier relate to it is unknown.
Humans are unusual, because unlike most sentient creatures in Slayers, they are not as a group automatically aligned with either the shinzoku or the mazoku. (Unlike the ryūzoku, for example.) There still exist an overall sympathy towards the shinzoku, who are generally worshiped as gods by humans, but this only very rarely manifests itself as a military alliance.
The human society and culture in Slayers vaguely resembles that of medieval Europe, although the existence of several institutions or practices are glaringly anachronistic. The society is surprisingly egalitarian as well, with men and women found equally in positions of importance and power. Some cultural traits show a wide range of influence, most notably Japanese, but other references such as Arabic can also be observed.