Responses
I'm not sure if this is a spin off (it could be but I only know this one) but this is similar to your description
https://www.mangago.me/read-manga/hana_no_akuta/
Big thank youuuuヾ(☆▽☆) it was the same author ლ(´ڡ`ლ)
So this bl goes like this, it's a oneshot manga also a spin off(if I'm not wrong) i can't remember the plot, but the character was like uke is white hair and the seme is black hair. They are like a mafia and the seme is the assistant or partner in crime of the uke( or something like that) i think they have 4 oneshot.....thanks(づ￣ ³￣)づ