The phrase (likely a stylistic or corrupted spelling of "milf kings" ) appears to be associated with R-18 adult fiction and web novels , specifically within subcultures of Webnovel .
There are various streetwear and novelty apparel items (often called "pieces" in fashion) that use provocative "MILF" branding or graphics.
The term is often found in the tags and descriptions of adult-themed fantasy novels, such as those involving "MILF systems" (a gaming-style progression mechanic for adult encounters).