Representing identity in games
As soon as a player can customize themself, or play as a character who isn't fully defined already, there is a degree of agency in the player character. And if that's the case, identity comes into play.
It's valuable to allow players to state their gender, for online or even solo play, to feel represented. But let the player decide the side effects of it instead of making assumptions, both because it's inconsistent and because new genders are ever-evolving.
Body gendering and gendered language
For body representation, either:
Don't include gendered features of the body, or
Let the player choose their gendered features. Don't gender the selection and don't tie cosmetics to gender
For body attraction, don't restrict player choice. Let them decide how others react to them:
Don't include romantic or sexual interest, or
Let the player choose how others should be attracted to them. Don't make it about the body here, only gender. Allow the player to set romantic and sexual attraction preferences separately, and have "none" as an option for both, to support both aro and ace players
For gendered language such as "hey champ", either:
Let the player choose the gender association used with them. This is separate from pronouns because gender and pronouns aren't necessarily tied
Characteristics and backgrounds
There are also assumptions about the player to avoid when it's not relevant to the story, including their language(s), ethnicity, skin tone, religion and political leans, diet and economic status. Christmas and marriage pop into a lot in particular, and disadvantages for avoiding meat (like how in Minecraft, you starve early game without meat).
Earlier I mentioned gendered word choice, and that comes into play here (a lot), both spoken and written.
If surnames are used, "Mx" exists in English for those who don't want to use Mr or Ms, and the long form can be Mixter or Misster.
In non-English languages, age and familiarity can be a lot more dramatically involved.
Some languages use pronouns and others use conjugation for gender. The first is easier to localize for, but you can use suffixes and lists of irregular words to handle the latter case (if you really want to). Localization can't handle everything, so I recommend defaulting to the player's name in that case.
Most games just say "Player", the player's name, or make them pick a simple he/she role (if they make a choice at all). But pronouns can be supported, in which case the player should be allowed to write in their own. I suggest also providing default sets; I used this resource. On top of that:
Names append 's for possessive case, e.g. "Her" and "Hers" would be Eve's and Eve's, but other cases (She, Herself) are still Eve
Those cases don't cover everything, there are these self pronouns, which differ based on plurality. This is important to support systems:
We, us, our, ourselves, ours
Names append 's for possessive case, e.g. "my" and "mine" would be Eve's and Eve's, but other cases (I, me, myself) are still Eve
There are also subject-agreement words, which I've collected most of. The apostrophes are contractions of would, are and have, in that order. There are other contractions like "will" as in "she'll", but only those that change are listed here:
is, was, has, 'd, 's, has for other (single) such as "she is"
are, were, have, 'd, 're, 've for other (plural) such as "they are"
am, was, have, 'd, 'm, 've for self (single) such as "I am"
are, were, have, 'd, 're, 've for self (plural) such as "we are"
Names use the "other single" tense, but don't contract for is.
s is suffixed for many verbs to match pronoun collective status, e.g. "he wants" instead of "they want"
There are a few special ways to handle pronouns that players may like:
Only using the player's name
Alternating between chosen pronoun sets, especially "he" and "she"
Randomly picking a pronoun, which helps for multi-gendered and gender apathetic players
It takes a sophisticated model to represent any realism in plurality, but I'm trying this and it would be cool to see more of it. First:
Anything related to the mind becomes an aspect of each headmate, such as name, gender, preferences, skills and associations. When multiple headmates front, suitable mixing should be done
When a player prefers to use names and there are multiple headmates fronting, they should be referred to as a name list or collective pronoun like "they"
Interactions need to be set up based on headmates instead of plural systems, so that all reactions are applied based on the headmate, especially for the player
Headmates can be fronting, partially fronting or not at all
Most of that is just moving player details into the model of a system and their headmates, and the player could choose when headmates are fronting. A more sophisticated model could take into account:
Allowing headmates to observe or share influence independently
Allowing headmates to be known to the system, anonymous, or not
Trying to model system functions and interaction between headmates, such as who fronts, shy or pushy fronts, blending, etc.
A reactive system to simulate the natural switching of headmates
Feel free to make suggestions and corrections!