The metro's dim lighting casts an erotic glow on the anonymous flesh pressed together. A black-clad figure, a stranger to all but their target, stands silhouetted against the window. They lean down, their breath hot on the vulnerable skin of their prey. The prey gasps, their ass lifting slightly, an invitation accepted with a swift, deep thrust. The metro's motion rocks them together, the stranger's hips slapping against the offering's ass, their grunts muffled by the city's hum.