One of the coolest OC breathing styles I've brainstormed is 'Frostbite Breathing'—imagine slashes so cold they freeze demon blood mid-air, leaving glittering ice trails. It'd have forms like 'Frozen Lotus Waltz,' where the user spins like a blizzard, or 'Aurora Piercer,' a stab that refracts light into blinding colors. The downside? Overuse could give the user hypothermia, adding drama. I love how it contrasts with Flame Breathing's heat, making it perfect for a stoic, winter-themed character who slowly thaws emotionally.
Another idea is 'Echo Breathing,' where attacks reverberate like soundwaves, disorienting demons by disrupting their senses. Forms could include 'Resonating Howl' (a scream-powered slash) or 'Silent Sonata' (a delayed strike that hits after a pause). It'd suit a musician-turned-slayer, maybe someone who lost their hearing but fights by 'feeling' vibrations. The style’s unpredictability would keep demons guessing, though mastering timing would be brutal.