I spent way too long staring at the Tokyo colonies arc trying to pin this down. Mahito's worm is, like, his whole thing? It's not just a tool, it's the core visual of his Idle Transfiguration. When he manipulates a soul's shape, that wriggling thing manifests. It's the literal connection point between his will and the target's soul, the needle and thread. But evolution? Okay, so early on, he's poking people one-by-one, needs physical contact. Then we see him spawn miniature versions from his hands, right? That's the worm tech evolving from direct injection to ranged projection. It's his technique becoming more refined, more versatile, less about raw touch and more about controlled emission. The worm is the technique's expression.
What really gets me is the 0.2-second domain expansion. He doesn't just blanket the area; he shoots out a single, massive worm-thread that tags everyone. That's the peak. He condensed the essence of his technique—that soul-manipulating filament—into one instantaneous, wide-range attack. The worm went from a hands-on sculpting tool to a conceptual weapon. So its role in his evolution is everything; as his understanding of the soul deepened, the worm's form and function transformed to match. It's the evolving symbol of his cruelty.