A homunculus (artificial human), a living weapon, created by Hibiki. Hibiki created her for Yutsuko, who attempted to replace her dead child with an homunculus, but only created unstable blob-like creatures, which disappeared after three days.

After some work, Hibiki and Shirotsuki create a homunculus. While at first very bratty and naughty, she later gets along with Hibiki and the two develop a warm relationship. However, Shiraasan is still an incomplete being, and her life is placed in risk.

Later, her existence is stabilized and she becomes something of a sister-daughter to Hibiki. She lives with Hibiki and often becomes involved in her mishaps, along with Ahito.

As a homunculus, Shiraasan is a living weapon. Her power allows her to materialize guns and other such weapons. When her powers are used, her pupils narrow. However, because she is a magical existence, overusing her powers can cause her to disappear.