The phrase translates from Japanese roughly to "staining older sister's provocative body with thick white fluid." It is a highly specific, explicit tagline typically used in adult Japanese media, including anime, manga, light novels, and adult video (AV) marketing.
A colloquial Japanese term meaning "lewd," "perverted," or "sensual." It is frequently used in lighthearted, ecchi, or explicitly adult media to describe a character's physical appeal or a specific suggestive scenario. oneechan no sukebe body o hakudaku ni someage hot