Sysling

Not to be confused with syslet.Sysling:

A sysling (portmanteau of system + sibling) is a headmate that is related to one or more headmates in a system. This can be due to a single system member splitting into separate people, multiple shard seeds growing at the same time, or syslinghood can simply describe a close relationship between two or more headmates (like how a friendship can be so close that the friends consider each other siblings).

Syslinghood can also come from fictional siblings from any sort of media forming in the system together, or syslings can be formed by system members having children of their own outside of splitting or the host planting shard seeds. Any system type of any origin can have syslings or an otherwise sysling relationship (or multiple all at once).

Syslings are more likely to be affected by order effect, are more likely to be hosts and even share that power, or they can fill any role, or be without a role. It's important to remember that dynamics and overall relationship between in-system siblings are often just as complex as they are between siblings in the external world. Even if, for example, a fictional set of siblings from a piece of media are introjected, that does not always mean they'll share that exact relationship.

Subterms

 * Splitling: Syslings that come from the splitting of a headmate into multiple headmates and consider each other siblings.
 * Shardling / Seedling: Syslings that originate from the practice of a headmate, usually a host, purposefully taking pieces of themselves so that they can become their own sentient people.
 * Systwin / Syslet / Sysdruplet / etc. : Syslings created/formed/split together within minutes/days of each other can consider each other to be this. They can resemble fraternal or identical twins/triplets/quadruplets, and so on).

Related Terms
This may be considered a type of dualter.

A form partner is a headmate that formed or was discovered at the same time as one or more other headmates, and may be a sysling of those headmates.

History
The HorrorCrux Collective and The Etheridge Collective joint coined this term searching for a term that best fit their experiences.

An example of syslings are Chokuto, Kodachi, and Makibishi of the Etheridge Collective, born within minutes of each other and are co-hosts.