Minako Yurihara is a student at Shinyo Academy and is regarded as the top student in the school, widely considered a genius by her teachers. Her exceptional academic ability, however, isolates her from her peers, who ostracize her, leaving her a reclusive girl with no close friends. She has straight, long black hair and brown eyes. Her role in the story is defined by two distinct but intertwined identities: the original human girl and the entity that assumes her form. The real Minako Yurihara is murdered and consumed by the Manticore, an artificial human created by the Towa Organization as an imperfect clone of the alien entity known as Echoes. After killing her, the Manticore takes on her appearance, using her identity to infiltrate Shinyo Academy and blend in with the student body.

The Manticore, operating under the guise of Minako Yurihara, is a predatory being with the ability to transform its appearance, having the same shape-shifting power as Echoes. It also possesses the unique ability to produce drugs within its own body, which it uses in conjunction with its human ally, Masami Saotome, to further their goals. After Saotome discovers the creature, rather than fighting or fleeing, he convinces the Manticore that it would be more beneficial to spare his life and assume Minako's form, and over time the two form a deep bond, working together on a plan to control humanity through the production and distribution of an addictive drug known as Type S. The Manticore kills students both for sustenance and to experiment with its drug, drawing the attention of Nagi Kirima, who is investigating the disappearances, and eventually of Boogiepop. The creature is driven by a primal instinct to survive and preserve its own existence, as it was created imperfectly and fears being destroyed by its original counterpart, Echoes, or by the organization that made it.

The original Minako Yurihara, before her death, is characterized by her isolation and brilliance, a person whose talents set her apart and made her a target rather than a friend. The Manticore, in her form, displays a calculating, predatory nature that is initially focused on survival but later becomes more entwined with her partnership with Saotome. Key relationships are central to her narrative. The most significant is the bond between the Manticore and Masami Saotome, which evolves from a predator-and-victim encounter into a mutually dependent partnership and, according to the source material, genuine love. She also has an indirect connection to Echoes, her original template and the being sent to stop her. The only relationship the real Minako had was the distant, unreciprocated admiration from her teachers and the social rejection from her classmates, leaving her profoundly alone before her death.

Development for the character is split. The human Minako Yurihara has no development beyond her tragic death, serving as a victim whose identity is stolen. The Manticore, however, undergoes a transformation from a desperate, survival-driven escaped experiment into a more confident, ambitious entity that, alongside Saotome, seeks to wield power over others. Its destruction by Boogiepop, with an arrow fired by Shirou Tanaka, marks the end of its arc. Notable abilities associated with the Manticore while in Minako Yurihara's form include complete shape-shifting to replicate physical appearances, the internal production of psychoactive substances, and a voracious, predatory nature that the series explicitly labels as man-eating. The real Minako had no special abilities, her only notable trait being her extraordinary academic talent.