In the film, it’s verbally spoken between Liu Kang and Kung Lao that they are cousins to each other.
I didn’t realize it until the film had done it, but the concept of Liu Kang and Kung Lao being direct cousins was a very interesting, neat and clear cut way to explain their relationship with each other without going into a lot of detail. It was also another almost perfect way of transitioning the history of their relationship in the games onto the big screen. Of course, they should’ve gotten more exposition (as most other characters should’ve), but that dialogue when they first met really surprised me because it felt right, not just to the fans of the franchise, but also regular viewers of the film who’d have no clue who these characters are.
As most of us know in the usual iterations of the characters, Kung Lao and Liu Kang are Shaolin Warriors who are really good friends. So good of friends that they’d risk their lives for each other and that’s why, (another spoiler) when Kung Lao gets his soul sucked and Liu Kang doesn’t get to help him, it really didn’t feel like that was the best choice in writing. Sure, it gave Liu more of reason to be something that wasn’t a droning robot of divine respect for the oh-so-great Lord Raiden, but it just didn’t feel necessary or the right thing to do for that character’s story arc. It felt like a direct callback to the beginning of the 1995 Mortal Kombat movie where Liu lost his brother to Shang Tsung taking his soul, except in this movie… it just feels like we only lost another character rather than someone who is supposed to be very important to the story.
I don’t mean to undermine Kung Lao’s relevance and importance in the story, but it feels like that’s all I can do because he was set up that way. It hurts because after watching the film a couple of times, you realize what he is… disposable. Just as many other characters in this film are. Nitara, Goro, Mileena, Reiko, they’re the disposable villains. The only thing that separates them from the disposable heroes (those being Kung Lao and Kano, if you’d consider him to be a “hero” in the film) is that the disposable heroes are disposable with reason, or as I’d call it “disposable within reason.” Once Kung Lao and Liu Kang help Kano discover his arcana, Kung Lao immediately becomes less than a supporting character. That was the end of his importance in the movie. He had a reason, fulfilled it, and then died. Kano was the same. He had REASONS (get the heroes to the temple, destroy the staff), fulfilled them, and then died. Remember, a big part of Kano’s story was discovering his arcana, but the main part was losing it. As less important as that part may have seemed, it’s what gave Sonya another reason to be in the story (that was actually valid other than her reason being a skeptic who has some evidence to back it up).