Omega, as the last letter of the Greek alphabet, often symbolizes endings or finality, so its opposite in mythology isn't a single figure but a concept tied to beginnings. I'd argue Alpha, the first letter, is its natural counterpart—think of primordial deities like Chaos in Greek cosmogony, the formless void that predates creation. But mythology loves duality, so you could also consider cyclical opposites like the Ouroboros (the serpent eating its tail), where endings birth new beginnings. Norse mythology's Yggdrasil, the world tree constantly decaying and regenerating, feels like a living rebuttal to Omega's 'finality.'
Honestly, I vibe more with the idea that Omega's true opposite isn't another entity but time itself—specifically, timelessness. Eternal beings like the Hindu god Shiva, who destroys only to recreate, or the Phoenix reborn from ashes, defy Omega's closure. Even in modern stories, characters like Doctor Who's Time Lords toy with Omega's linearity by rewinding destinies. It's less about a 1:1 mythological matchup and more about how cultures frame eternity against endings.