I’m not the DM- there isn’t one.
Explanation: For a variety of reasons, I am continuously creating characters for various RPGs, even if I’m not currently in a game using the system. It helps me maintain or increase familiarity with those systems or settings. It helps me “stay engaged” with the hobby. It helps me remember character ideas I think are “cool” or “fun”.
Sometimes, I even work out the mechanics of a character in multiple systems and genres. The first was a character named “Slapstick”, a mercenary who wore “clown” makeup and wigs fo mess with the minds of those he fought. He was statted out in RIFTS, HERO, Torg, GURPS, 2Ed D&D, and at least one Mecha-centric RPG (the group was playing several of those, soooo...).
Tangentially, it also helps me round out characters for pieces of fiction I write- usually such designs are done in HERO.
So when I do one of these Brainstorm threads, it’s usually because I had an idea I thought was really cool, but for some reason, was struggling with either the actual mechanics of realizing the concept or I‘m trying to translate the character from one system to another (which may or may not be related).
And because of all that, I try not to venture too far into the woods of GM judgement calls when doing a design. Regardless of how outré the concept is, I try to stay within the RAW or consensus RAI of a given ruleset. I’d rather a GM reject a PC in its entire than over some difference in opinion on what is “legal” in a given campaign.
(And I rarely design NPCs that break rules that my players can’t.)