Shiwasu no Okina is a Japanese manga artist and illustrator recognized as a leading figure in the adult manga industry, with a career spanning over twenty-five years. Born on August 29, 1975, in Yamaguchi Prefecture, he currently resides in Kanagawa Prefecture. His professional pseudonym translates roughly to The Old Man of December. His career began while he was still in high school, participating in doujinshi (self-published) activities before making his formal debut in 1997, when he was selected for the COMIC Aun Newcomer Award and published his first work, Get or Die, in the same year. He has since become a primary contributor and a signature artist for the monthly magazine COMIC Aun.

Shiwasu no Okina is the original creator behind numerous manga series that have been adapted into anime. Among the most notable of these adaptations is the anime Peace Hame!, an OVA series based on his manga of the same name. He is credited as the original creator for the Peace Hame! anime, which was released in 2012. Other works of his that have been adapted into anime include Nudist Beach ni Shuugakuryokou de!! The Animation, released in 2016. In addition to these, he has a substantial bibliography of original manga. His most famous long-running series is Shining Musume, which achieved notable success with a serialization spanning seven years and totaling seven volumes, an exceptional length for its genre. Other significant original works include Enkou Ojisan, Please! Freeze! Please!, Healing Touch, and the series JC Ecchi, among many others.

The artistic identity of Shiwasu no Okina is defined by several recurring themes and stylistic trademarks. He is renowned for his high technical skill and distinctive, polished art style that has evolved significantly over the course of his career. His work frequently features inventive and often bizarre storylines that incorporate supernatural elements like magic or psychic powers, and are known for their unexpected and absurdist conclusions. While his narratives often begin with plausible scenarios, they are famous for developing into chaotic and expansive endings. A signature element of his work is the depiction of large-scale group scenes, which are a hallmark of his bold panel composition and direction. Despite the adult nature of his work, his stories frequently conclude on a comedic or happy note, avoiding consistently grim or violent resolutions.

In terms of industry significance, Shiwasu no Okina is considered a top-tier and highly influential creator within the adult manga community, with a prolific output and a long-standing career that has garnered a loyal international following. His works have been translated into multiple languages and published around the world, and he has also worked as an illustrator, providing cover art for other manga titles. Beyond his commercial publications, he remains active in the doujinshi scene, operating under circle names such as Okina Project. His influence is such that he has been invited as a featured guest at major fan conventions like Anime Expo.