Depending on what sort of tattoos you'd like to be able to support, off the top of my head, there's:
- Where are they on the body (arms, back, face, wherever)?
- How big are they?
- How visible are they? Are they under your clothes or can they be seen even when you are fully clothed?
- What is depicted in the tattoo? Is it a picture? Is it an artistic pattern (e.g. tribal tattoos)? Is it some text? Is it something specific, like one of your SO's names or faces? The devs would have to limit this to a finite amount of possibilities.
You'd need to store all this information somehow. And potentially for many tattoos in different places. You also might want to keep track of how much of a character's skin is covered in tattoos. Also, this stuff combines with different skin types and body types. If you have fur or feathers, do they cover your tattoos? Are there skin types that make it difficult or impossible to hold the ink for tattoos? Can you get tattoo-equivalents by permanently dying your hair, fur, feathers, etc in particular colour patterns? What happens to your tattoos when the body part they're on gets transformed into something else?
You have to put all this stuff into the appearance descriptions used for your character.
But putting tattoo information into code is the easy part (relatively speaking). If you
really want to have the game "support" tattoos, then you want characters/scenes to be able to recognise tattoos. Which means writing text to take into account all the different possibilities above. For example, should Syri say something if you have her name inside a heart tatted on your arm? Should Anno say something about it? What should she say if you both Syri's and Anno's name on you? What do other people say about them? Should people say different things depending on where the tattoo is or how big it is or how obvious it is? What if it's a picture of them instead?
You could have a dom, let's use Sera as an example, demand that you get something like "Property of Sera" tatted on you. And be happy if it's there, or get upset if you get the tattoo removed.
So even if you put in the work for characters to have tattoos, there's a good chance they'll be mostly ignored by the game. But to be fair, a lot of transformation types are already mostly ignored. From what I've noticed, characters mostly seem to only react to Steele's genitals (what they have or don't have, their size, and sometimes their number), Steele's apparent gender (masculinity/femininity score, etc), and Steele's race.
And, of course, you need methods for how the character gains tattoos (including picking out the details you want), and how they get removed.
If you wanted to keep things simple, you could just have "tattooed" as a skin flag that can apply to different body parts, and ignore what those tattoos depict.
You can get "a sleek black barcode" "printed on your ass" as part of the sub-tuner content on Uveto, which is more or less a tattoo. It's implemented as a perk, which means it doesn't show up in any of the description text.
