The angelic demon isn't really about some simple yin-yang duality anymore, at least not in the stuff I'm drawn to. It's this fascinating tool for confronting societal and internalized morality. The demon with angelic traits, or the fallen angel who kept their compassion, they force the narrative to ask: what even IS evil? Is it the species, the heritage, or the choices? I saw this done in a way that messed me up in 'The Unchosen', where the main character is literally born from a demon lord but raised by a celestine order. Their internal conflict wasn't just 'oh no my dark urges', it was a complete crisis of belonging and purpose. Are they betraying their nature by healing people? Or are they betraying their upbringing by feeling at home in the shadows? That tension is way more compelling than a simple battle between two sides.
Honestly, I think the trope shines when the 'good' and 'evil' aspects aren't separate forces warring, but a single, confused identity trying to build its own moral code from contradictory legacies. It moves past exploration into actual construction. The character isn't just discovering who they are, they're deciding it, piece by painful piece, and that's a process readers can graft their own struggles onto, even without the wings and horns.