Maria Tarō Sekiutsu, an illegal immigrant of unspecified nationality, purchased the birth certificate of a male student named Tarō Sekiutsu to attend Japanese high school under his identity. Most characters refer to her as Maria, though Kafuka Fuura uses the nickname "Mataro." Her adopted name "Sekiutsu Tarō" stems from the Japanese phrase "seki uttaro," translating to "I'll sell my name" or "You sold your own register, didn't you?"—a direct nod to her identity transaction.

Physically, Maria has dark skin and short hair, standing as her class's shortest student. Her uniform fits poorly, appearing too small for her frame. She displays wild mannerisms and a distinct aversion to shoes and panties, frequently appearing barefoot.

Characterized by extreme optimism and an innocent, immature personality, Maria often acts on misunderstandings, resulting in eccentric behavior. Having endured severe poverty, she is captivated by Japan's material abundance and compulsively hoards food or discarded items scavenged from the ground or trash. This habit, combined with her impoverished appearance and illegal status, frequently elicits sympathetic offers of aid from others.

Her unwavering positivity aligns her closely with Kafuka Fuura, forging a strong rapport between them. Maria consistently wears a bright smile that motivates people to protect or provide for her. Legally registered as male due to the purchased birth certificate, her biological sex is female.

Her role remains consistent as a supporting character defined by her immigration status, economic hardship, and distinctive behavioral traits.