MK1 Headcanon Dump (Non-Romantic/SFW)
Kitana and Smoke are the babies of their respective teams (from now on to be known as Team Umgadi and Team Lin Kuei). Kuai Liang is younger, but Smoke, being kidnapped adopted, is their honorary Baby Brother.
Kuai Liang's fiery powers come from their mom, who, to the Grandmaster's surprise, is/was a pyromancer.
Syzoth is the honorary fourth Lin Kuei boy. Bi-Han, Kuai Liang, and Tomas Vrbada have taken him in.
Even in his human form, Syzoth's skin gets dry, itchy, and scaly when it's time for his true form to shed.
Johnny Cage can be the meanest motherfucker in the world when he wants to be.
The Outworld throne is matrilineal, and a prince can't become king unless he has no sisters. The realm's many cultures vary on this matter, but the capital and big cities lean matriarchal. Rain feels a little henpecked at times.
Mileena has a military career, judging from the armor she wears in the Umgadi group shot. She's gone off to war more than once, leaving Kitana and Sindel to worry themselves sick over her.
Kitana is an excellent spy. She follows Mileena into the most sensitive places in Outworld, and her calm presence puts people at ease, especially around her hotheaded sister. She's also the best eavesdropper in Outworld, but you didn't hear that from me.
She also happens to have the most sass out of the entire roster.
Li Mei's shishi (Chinese lion) is female. Yes, there's a mane, but the critters often guard establishments in opposite-sex pairs and show no apparent dimorphism. How do you tell them apart? The male has his paw on a ball and the female has her paw restraining a cub.
(I'm trying to get some good Tanya ones, I promise, but they're mostly romantic/NSFW. She does have amazing skin with a jealously guarded beauty routine, and Mileena is a point of contention between her and Kitana.)
Kitana doesn't go to war unless Mileena asks her along, and even then she won't let Baby Sis on the front lines. Kitana keeps her skills sharp by helping to train new military recruits.