An adaptation of a children's novel of the same name published in 1973. Endo Hiroko is the author, who was inspired to write the story from a tale her father told her as a child.
It follows a 13 year old girl named Aki. During a pilgrimage to Sensou-ji (a Buddhist temple located in Asakusa, Tokyo), she found a mistake in the sangaku. News spread quickly of her intellect and eventually landed upon Arima Yoriyuki, the lord of the Kurume Domain (he himself was famous for finding the rational approximation of pi). He hired Aki to become an arithmetic teacher for the region's princess, but hired others as well. In a math competition, Aki fought against other geniuses and prodigies, all for the hopes of earning a wage so that she may one day open a school for poor children so that she can teach them arithmetic as well.