Upper Moon OCs? The power creep is real, but the fun is in the justification. I get annoyed when it's just 'they ate a lot of demons' without any deeper lore. The best ones I've seen tie their power directly to a specific, horrific theme that mirrors the official Upper Moons—like a demon whose Blood Demon Art manipulates sound and memory, growing stronger by literally consuming the 'echoes' of trauma from villages. Their power isn't just a number; it's a narrative device. You need a gimmick that feels uniquely theirs, something Muzan would find useful enough to grant more blood.
Another angle is the slow corruption angle. Maybe they started as a lower moon obsessed with a single craft, like sword-smithing or poison-making, and Muzan rewarded their twisted 'dedication' over centuries. That feels more earned than random power-ups. The weakest OCs are the ones who are just stronger versions of existing characters. Give me a weird, niche specialty any day.