Loners is the collective term for individual wolves not presently a member of any active pack ranks. As this is not a pack or an official group—just a term of reference for lone wolves—there are no leaders nor foundation date, and while lone wolves may travel in batches or adopt a title for themselves, they are not considered within pack unless it is formalized and recognized by the 'Souls Assemblage. In short, loners are just the random wolves that float around 'Souls, whether temporary and looking for a pack to call home or permanent and just too cool for packs. At any given time there are tons of NPC loners floating around 'Souls, although they are often neither named nor listed in any particular place ICly or OOCly.
A loner is a canine who does not have a pack. Typically they are not prohibited from trespassing onto a pack's claimed lands, although some packs and their leaders may be more lenient, such as Ichika no Ho-en back in its day. However, no pack will allow a loner to repeatedly trespass through their lands, although waiting at marked borderlines and calling for assistance is generally preferred. Loners should take care to avoid the interior of packs unless accompanied by a ranking member as escort or a leader's permission. That said, a loner must generally fend for himself for food, a place to sleep and against predators—a very difficult task to do. Their lives are not easy, and it is highly encouraged that loners join a pack to aid in their survival. Loners tend to get dead a lot faster than ranked characters.
Historically, there have been plenty of loners who did well enough on their own. Some players might find it easier to get plots for characters within a pack though, so if you find yourself constantly short of threads, it may be time to look into joining a pack. That said, some characters just do better as loners, some examples being Laruku Tears, Barrett, Cassandra Asylum, and Judas Poer de Aika XIII. It is still encouraged that a loner joins a pack, especially one that may be struggling with a low member count. Make sure to check the Rank Listings.
Loners are allowed to thread freely in unclaimed lands (Neutral Territories). As mentioned, they are not allowed to trespass into pack lands. To assume they passed borderlines undetected is considered powerplay, and doing so should be limited and aware of severe in-character consequences that may result in attack or death. Usually, these circumstances are plotted in advance between players, but are uncommon or rare in occurrence around 'Souls.
Loners can live or travel in groups but may not claim any land as their own. Some may defend a small area, such as a building or a house, and take of residence there, but the home may be lost in the case of a pack claiming the territory. Residential disputes like these are not terribly uncommon; for example Søren Rask was kicked from his northern home by Sangi'lak leaders upon migrating territories in mid-2013, despite attempted in-character negotiations. At the time he lost custody of the homemade forge built in his home, an unfortunate risk and downside of being a lone wolf. Any homes or buildings are fair play for loners to "claim" if it is not in another pack's territory; places like Halifax, which cannot be claimed by a pack, are a common destination and one big enough that Judas Poer de Aika XIII, Basil Butler and Belial Massacre, for example, each lived there at the same time but never interacted.
Unnamed loners are common NPCs for threads, usually used as means to develop an active character, in which case the Preybot may be used. In the past, unnamed loner NPCs have been used to trespass on Inferni's borders or getting into fights with members of the clan. Hybrid Holocaust and Kaena Lykoi actively sought out a lone wolf with the intent of murdering it. Given this history, it would seem as though being a loner is very risky business.
Loners that want to leave 'Souls cannot be set to NPC for any amount of time. As a loner, it is more likely they left or are not performing any notable tasks that would allow for an NPC status. In order to maintain NPC status on the board, a loner must join a pack or become the cNPC of another active member; they automatically join the pack of any pack member they cNPC to, whereas if they become the NPC of a loner they would remain the same.