Plurality
You are a plural system with (IE)d4 additional personas (often called “headmates” or “alters”) sharing your consciousness, or “headspace.” Each alter can vary widely in preference, expression, orientation, gender, species, or even be more of an abstract concept, fictional character, or famous figure. Alters may have varying degrees of awareness of, attitude toward, and communication with each other. Alters usually alternate fronting (controlling the body and communicating externally), although co-fronting (multiple alters fronting at the same time) is possible, sometimes blending together while co-fronting. Some alters may never front but are still aware and communicate in headspace, and alters have different relationships with each other as any other social group does
The player cannot choose when to change which alter is fronting. (Such attempts will likely lead to Pain (Head) or Brain Fog.) Different alters tend to have circumstances by which they front, but not always, and alters can sometimes disappear for extended times. The player and GM may want to create a table of triggers that cause a shift in fronting, both triggers known to the character and seemingly random triggers known only to the GM. Note that the alter corresponding to a trigger may not be whom the player or party considers optimal, such as an alter with a phobia who always fronts and runs away in the presence of that stimulus while another with proficiency in Medicine may front at the sight of blood.
Alters may also communicate in headspace when not fronting, speaking to each other and to whomever is fronting but only audible in headspace. If you have at least one alter who can communicate with whomever is fronting, that alter can use their help action to give you advantage on Wisdom (Insight) checks.
When shifting which alter is fronting, if shifting to a cooperative alter who’s usually co-aware, the new alter can front without penalties. If the new alter has Amnesia relative to the previously fronting alter, they need a moment to assess the situation and will respond accordingly. If in combat, the disorientation requires one round, after which they act on initiative 1 with appropriate modifiers.
Over time, additional alters may appear. 1d4 days after life-changing events such as the end of a traumatic event or the end of a major adventure or campaign arc, roll 1d20. On rolling (IE) or less, you add another alter. This splitting is often accompanied by headaches, blackout, memory loss, and disorientation, and the new alter is usually confused when fronting for the first time.
When creating a plural system as a character, alter stats may vary, up to ±2 from the base stats, but should total the same number as the base. Alters may share a character class or have different classes and proficiencies for each (or some combination). Treat the character as multiclassed for level advancement, or keep separate experience points for each alter based on who was fronting during a given encounter or story beat. Some alters are likely noncombatants or may even be children. Or the player and GM may decide that all alters share an experience pool like a typical multiclassed character, depending how aware any given alter is when not fronting.
If you have other traits, you may assign them to one or more alters, both mental and physical. You may choose Amnesia (Anterograde), Amnesia (Traumatic), or Traumatic Flashbacks as one or more of your other traits for one or more alters. Note that awareness can vary by individual alter or groups of alters, so Amnesia may cluster, certain alters being aware or co-fronting while other alters have no memory of that time. Other Amnesia (usually Traumatic) may be universal to the entire system.
Plurality in the past was often called, “Multiple Personality Disorder,” but that term does not accurately describe the plural experience and is no longer used. Because plurality has as many expressions and variations as systems who experience it, including varying forms of cooperation and Amnesia, if you’re interested in representing a plural system, check out the Plurality Hub or Multiplicity and Plurality Wiki, and talk to your GM about your system and what modifications to these rules would be more representative.
Real-world Examples
Plurality (Parogenic, Endogenic, Gateway, Quoigenic, Paragenic, Traumagenic), Dissociative Identity Disorder
Assistive Options
Plural systems mostly need understanding from those around them and willingness to acknowledge the different alters as individuals the same way they would acknowledge multiple singular people. It’s helpful when communicating with a system to verify who is fronting but also to recognize that those not fronting are often conscious and aware of the external environment. While your physical appearances may change when switching alters (such as posture, facial movement, voice, or gait), each may sometimes use a visible accessory to help others know who is fronting, such as a pin, hat, or scarf, or an accessory may move from one position to another.