Depends on the verse! In their (current) main verse, Katya is a vampire slayer that goes to Mokrija to avenge her mother (who Nikolae killed to bait her) and ends up being trapped there by Nikolae for a long long time. There's a lot of fucky shit that happens, including her killing Nikolae and sending him to hell (which doesn't stick because the devil ejects him back into the mortal world because he hates his vibes so fucking much,) Katya gets into a lot of witchy shit, becomes the lady of Mokrija, all that fun stuff. Also a lot of dubious and outright nonconsensual sex. Nikolae is obsessed with her, and she's got... very complicated feelings. Nikolae fully believes that they're soul mates, and Cal once told me that Katya is kind of bought into that in this verse which like... not to victim blame, but girl...

In the verse that we have for them with the steam punk trains (which is mostly what I draw for them these days) Katya as a child goes to the railroad to try to find her father (who's ALSO named Nikolai <3) and ends up meeting Nikolae instead. He takes her in as his "daughter," and as she grows older they end up in a very weird quasi-familial pseudoincestuous romantic relationship that makes everyone around them wildly uncomfortable lol. Katya acts as his second in command and enforcer, and is very brutal in her work. She's still a human for most of this, so Nikolae relies on her to be able to manage people during the daytime hours. Also, Nikolae in general is extremely lazy and would rather just dictate orders to people and let Katya actually handle running the trains. He is still very strong and capable though, again... just lazy lol. He loves and trusts her completely.

Anyway, yeah Urale and Callanin!!! They have a long friendship which is at time sexual. They actually belong to the same species of shifters, Urale just mostly keeps elfshape for various political and personal reasons. They do have freaky quadrupedal monster sex though. Urale's true form is similar in size to Callanin's, so they're both big and scary.