Miia is a lamia, a being with the upper body of a human and the lower body of a snake. She has long, vivid red hair, yellow eyes with slitted pupils, pointed ears, fangs, and a long tongue. A small patch of scales marks her cheeks, and her most visible trait is her long, red serpentine tail. She stands around seven meters in total length, with the snake portion accounting for most of that.

As the first liminal girl placed with Kimihito Kurusu under the Cultural Exchange Between Species Bill, Miia is a central figure in the household. She arrives naive and carefree but quickly develops an intense, romantic attachment to Kimihito, whom she calls darling. Her personality is active, passionate, and openly affectionate—she is a hopeless romantic who believes love can overcome even strict interspecies regulations. She can be clingy, especially when sleeping, and tends to wrap her tail around Kimihito for comfort. A notable quirk is that the very tip of her tail is highly ticklish, a vulnerability Kimihito exploits to free himself from her embrace.

Miia is sweet and innocent in many ways, yet she is also possessive and jealous of Kimihito’s attention, often trying to seduce him. She is catastrophically bad at cooking and housework, and as a poikilotherm, she becomes sluggish or immobile in cold weather if her body temperature drops. Her primary motivation is to be accepted in human society and to become Kimihito’s partner. This desire drives her throughout the story, pushing her to overcome her initial insecurity about her hybrid nature.

Her physical abilities stem from her lamia physiology. She has exceptional flexibility, can constrict objects or people with her tail, and possesses enhanced strength and agility. She is a strong swimmer and an adept climber, using her snake body to navigate efficiently. She is less effective in small or restrictive spaces, and her emotional state can affect how well she controls her powers. Over time, Miia develops from a dependent, clingy girl into a more confident and proactive character who actively protects Kimihito and her fellow monster girls.

The most significant relationship in her life is with Kimihito. He serves as her protector, love interest, and the anchor of her new life. Her interactions with other liminal girls in the house—Papi, Centorea Shianus, and Rachnera Arachnera—range from friendly rivalry over Kimihito to genuine moments of empathy and teamwork. Agent Smith, the government coordinator, acts as both a guide and a source of bureaucratic pressure. Miia’s role in the story is that of the first monster girl to bridge human and liminal society, and her journey shows her growing commitment to that world while never wavering in her devotion to Kimihito.