The Xenos are treated as targets by regular monsters and are known to fight them. They have also been targeted by adventurers unaware of, or uncaring for, the fact they are intelligent creatures, some of them even being sold on the black market. They search for their comrades in the unexplored areas of the dungeon. All Xenos have a strong longing for the surface and someday desire to reach the surface.
They are apparently reincarnations of monsters that have been killed multiple times by adventurers, as they have been shown to possess memories from past lives. They consume the magic stones of the monsters they defeat to strengthen themselves, with all of them being strengthened species, and some managing to reach a power well above the average level of their monster counterpart.
Although Fels first made contact with them around 15 to 16 years ago it is known they have existed for a longer time, as some are much older, such as Lyd and Ray, who were among the first of the group and are 20 years old. However, it is unknown precisely since when have they existed.
They hide in their Hidden Villages, which are unexplored areas of the dungeon. They refer to the dungeon as their mother, and believe it created the Hidden Villages to protect them.
When the Hestia Familia met them it was said there were 40 Xenos at the time. However, the number of Xenos that are currently part of the group is unknown, as it went down after the death of Wiene's group but it also went up after the Xenos captured by Ikelos Familia were rescued. In addition, it hasn't been said if more Xenos have joined since then.