Random SL and RQ headcanons go!
So, I like to imagine that the indigo steves have moth features (antennae and wings) HOWEVER, the ones that have lived in the Middle World and still do have moth wings made up of the blocks you can find in that dimension (half beds, bookshelves, crafting tables) that are held together by floating water in the shape of moth wings. Although, if the Indigo steve has lived outside of The Middle World for a long while (think a few years) then their wings would revert back to regular mothwings. I think that the type of moth wings would be whatever fits their personality the best.
For example, I have an OC named Pilot Indigo, he's lived outside of the Middle World for a long while and he now has emperor moth wings instead of the block filled ones.
The obsidian steves have runes that are engraved into their skin for identification purposes. These markings can mean a lot of things, like what their ranking is, their age, role, ect ect... Which also gave the silly idea of they'll make markings on their partner(s) to show that the person that they're with is with that obsidian steve. OH YEAH, another thingy I thought of with them is that they don't really have marriage, when you start dating one you just are stuck with them permanently, which also can lead to some wholesome interactions with a different type of steve wanting to be with their favorite obsidian steve and getting to witness said obsidian steve nervously having to explain that if they do that then there isn't really any backing out.
I feel like that interaction with Warrior Duo (Beef x Obsidian Captain) would be like this:
Beef: "Obsidian Captain, may I have the honor of being yours..?"
Obs Capt: *FLUSTERED OBSIDIAN STEVE NOISES*
Beef: ..??????
Obs Capt: "You are aware that you can't back out of this if we go through with this, correct..?"
Beef: "Whut-?" (<- He doesn't mind btw)
Another thing about the obsidian steves that I hc, they get really stiff when panicking, nervous, flustered, any really strong emotion tbh. So like, you could do something like flirt with or threaten one and you could watch them get really stiff and just s t a r e at you-
Another thing (wow I have a lot of obsidian steve hcs) is that they can make lava bubbling noises when they're happy. It's a lil frightening, but it's a good noise dw. Yet another thingamajig is that letting someone touch areas like their wrists, palms, neck, and chest are very big signs of trust since they're more sensitive and have important innards inside. Also, if one lets another person touch where their heart would be on their chest is the equivalent of the obs steve saying that they trust that person with their life.
Thank you for listening to my ramble :]