Balancing the powers in a half-angel, half-demon protagonist always hinges on internal conflict for me. It's rarely a clean, fifty-fifty split of good and evil. The most convincing stories treat the angelic power like a painful moral compass—it's not just healing light, it's a force that punishes you for violent thoughts or selfish actions. The demonic side offers easy, seductive solutions. I read one webnovel where the character's angelic wings would physically bleed whenever they lied, while their demonic power surged from that pain. That constant, visceral feedback loop was the 'balance'—not equilibrium, but a brutal tug-of-war.
Sometimes the 'balance' is more about societal pressure than internal struggle. The character might have to hide one heritage entirely, using angelic magic publicly while secretly relying on demonic abilities to survive actual threats. The tension comes from the fear of exposure, the constant performance. It's less about balancing powers and more about balancing identities, which I find way more interesting than another chosen-one-with-dual-mantles storyline.
Honestly, a lot of novels mess this up by making the character too powerful too quickly, giving them perfect control over both sides without any real cost. The best ones make the blending of light and dark feel unstable, dangerous, and deeply personal, not just a cool character sheet.