Cinematic 4K high-speed action sequence on the roof of a maglev train tearing through a mountain corridor at three hundred kilometers per hour. A whip-thin runner with a shorn scalp, a barcode brand behind her ear, and a hardshell jacket flaring open wields twin folding blades. She sprints the spine of the car, drops flat under a tunnel mouth, snaps up, cuts a boarding mercenary's harness, kicks him into the slipstream, vaults the gap between cars, skids sideways, blocks, ripostes, hurls one blade, catches a vent to swing under an overpass, then explodes back onto the roof mid-stride. Torn insulation and sparks streaking backward in hard lines, strobing tunnel lights slashing across her, panels peeling loose and vanishing behind, whip-pan tracking camera with speed ramps, 120fps snapping to 24fps on every impact, realistic wind-shear physics, extreme motion blur, ultra-high detail.