I've been following Biya since ~early '22 so I'll try to say as much as I know.
Kpring first seemed to be Biya's mentor figure regarding artwork, he's quite a bit older than her if I recall say like 5ish years. You can kinda tell by how similar their artstyles were and how they collaborated in pieces/conventions. It was kinda confirmed they were at least a close thing when on Biya's discord, she'd stream just a tiny bit and one time she went into kpring's room and playfully distract him (I remember he was playing Elden Ring so it was around when it came out). So take them living together as you wish, there's a non-zero chance they're siblings (but I doubt that).
From some speculation from the timeline and stuff, it seems they got together when Biya was really young (for Korean law standards I think?). So there's
that vibe for some people. I kinda just see it as a teacher/student love kinda thing and he's a lucky dude. Biya is/was legit passionate and great at art but the combination of her cosplay stuff and health sorta pumped the brakes on that really improving.
Anyways. They were an item and sometime around 2024 I think there seemed to be tension there? From what I remember there was a time they were separate but now they might be back together in a professional sense? I was there at C105 and kpring had his booth somewhere else with biya selling her photobook herself with another girl. To be honest I'm not sure what to make of their relationship right now because Biya really feels like a different creator nowadays with how little she draws
Edit: Below is a good place to start, also
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