This is a common Japanese given name or character name. In the context of online digital art and indie games, it usually refers to the main character of the series or the pseudonym of the creator.
Keywords like this typically originate from the booming Japanese indie subculture. Creators leverage global platforms to self-publish their niche projects directly to fans. Common Platforms for These Works niina no ero youbi shuumatsu wa himitsu ni touc work