An illegal immigrant of unknown nationality. She is nicknamed "Mataro" by Kafuka, although she refers to herself (as do most others) as simply "Maria". She purchased the birth certificate of a male student and is attending school under his name.

She is fascinated by "Japan's abundance" and hoards food and refuse she finds on the ground or in garbage cans. While Maria frequently displays wild behavior and an unusual abhorrence to panties and shoes, her impoverished appearance and illegal status, coupled with a bright smile, often encourage people to give her things.

The name "Sekiutsu Tarō" derives from seki-uttarō, which means "You sold your own register, didn't you?" or "I'll sell you my register". Because of their optimistic personalities, Kafuka and Maria get along quite well. Although Maria is legally a boy (since she bought the birth certificate of a male student), she is actually a girl.