The scream comes from Bleach, where Ichigo Kurosaki unleashes his Vasto Lorde form during his desperate fight against Ulquiorra in Hueco Mundo, a moment when his hollow power takes over completely. Fans clipped the roar from the anime and reused it far beyond that battle, turning it into shorthand for a character snapping, transforming or unleashing hidden strength. It keeps circulating in anime music videos, versus edits and reaction compilations because the sound alone carries the shock of that transformation, even for viewers who have never watched the series.