Sūgaku gāru

At the start of his first year of high school, the narrator meets a new classmate, a girl named Miruka. Without introducing herself, she gives him the beginning to number sequences, to which he answers with their continuation. One year later, the narrator is handed a letter by another girl, a new student named Tetra. The letter she wrote is a request for the narrator to tutor her in math. He begins teaching her, making Miruka jealous. The narrator balances his friendship with Tetra and his romantic interest in Miruka until Miruka and Tetra become friends after Tetra demonstrates her dedication to learning mathematics.