Born on July 26, 1965, Ran Masaki is a former Japanese AV idol, pink film actress, and gravure model who left a significant mark on the adult entertainment industry during the 1980s. She is best remembered as Nikkatsu's final "SM Queen," a title she held from 1985 to 1986, during which she became a defining figure in the studio's Roman Porno series. Masaki's career, though relatively brief, was notable for her commanding presence and her full-figured physique, which set her apart in an era dominated by more slender ideals. She starred in three Roman Porno films for Nikkatsu, two of which were written by the renowned bondage and SM-themed screenwriter Oniroku Dan. These collaborations cemented her reputation as a specialist in the genre, and her work with Dan helped define the aesthetic and narrative style of Nikkatsu's late-period Roman Porno productions.

Masaki's filmography includes notable titles such as SM Queen: Bondage Hell and SM Queen: Queen of the Whip, which showcased her ability to embody both dominance and vulnerability, a hallmark of the SM queen archetype. Beyond her work in Roman Porno, she transitioned into the burgeoning adult video market, appearing in several videos until 1987 that focused on her distinctive, full-figured body. These performances appealed to a niche audience and further solidified her status as a cult figure within the industry. Her career also encompassed gravure modeling, where her bold, unapologetic image resonated with fans of the era's more adventurous adult content.

A point of confusion in her legacy arises from some sources, such as the Japanese Movie Database (JMDB), which erroneously conflate her with Ran Mizukami, a pink film actress active during the same period who also performed under the fetish model name Sawako. While both women operated in similar spheres, they are distinct individuals, and Masaki's identity as Nikkatsu's final SM Queen remains her primary claim to fame. After her retirement from the industry in the late 1980s, Ran Masaki largely withdrew from the public eye, leaving behind a legacy as a pivotal figure in the final chapter of Nikkatsu's Roman Porno era and as a memorable icon of 1980s Japanese adult cinema.