I got a pair of sibling OCs and if you wanna do one out of the two, I'm cool with it! So, if I had to make preferences, it'd be them as BAMFs in a Jojo style! Dynamic poses would be pretty rad~ Aside from that, if you're gonna do only one, I'd prefer it to be the sister bc she's the main protagonist
Here's a beautiful sketch of the two generously done by @darlingGrim~
Further references hidden for the sake of keeping my comment shorter!
My references are all kinda done in Gachaverse, because it gets the job done for getting the basic look down lol 25 y.o. Haruka and 21 y.o. Mugen Kurogane are two siblings who work as demon hunters in modern-day Japan. The two reluctantly work together on the one-shot idea I have for it. Mugen prefers using a pistol and a taser gun from a distance, and Haruka prefers using Japanese short swords in close combat. She tends to be over-protective of him and he tends to over-think his actions when they get paired up together for a job. Little detail that wasn't captured in the sketch, but they both have a dark grey highlight/streak in their hair!