Nakadashi Leveling: Inherent Skill

It sounds like you're referring to a specific tag or phrase, likely from adult manga, games, or light novels. “Inherent skill” (or innate ability) + “nakadashi” (a Japanese term for internal ejaculation) + “leveling” (often used in RPG-style progression systems) suggests a fantasy or isekai setting where the protagonist has a unique skill that grows stronger through sexual acts, and “leveling” refers to the in-game or in-world mechanic.