I do have an idea for a colab, if you're interested; I have a character that's sort of a dark reflection of Y/n. Self-hatred, putting others before him, etc.
Though, the whole point of it would be to flesh out your characters, as my character is more aggressive; if K were to fight him it wouldn't end well. It could also help you get into the swing of writing of need be.
At the end of the day, my character is just a catalyst to help flesh out your world. A chapter that, itself, could be non-cannon, but provide insight to the characters of your world.
Let me know if you're interested, I'll contact you on Telegram.
And if you aren't, I understand, I just like writing with my characters and it could be used to help build up your world.