Create a moody key visual of a mecha girl standing on the rusted edge of a tilted steel platform over dark water. She has pale skin, ash-white hair in a high ponytail, matte gunmetal exoskeleton armor, glowing cyan coolant lines, and a massive rail cannon on her shoulder. Behind her, a vast derelict sea-city rises from the ocean in colossal silhouettes, with fog, dead cables, rusted towers, and bruised dusk light. Use cinematic concept-art lighting and a medium-wide shot.