"I" (Boku) love math. Just after the high school entrance ceremony, "I" meet a beautiful girl: Milka. Milka is a mathematical genius. She gives me many maths problems, she shows me many elegant solutions. Milka and I spend a long time by discussing maths in the school library. One year later, I meet another mathematical girl: Tetra. Tetra is one year younger than me, and asks me to teach her mathematics. While I teach her, she begins to understand mathematics and gradually to love its elegance. In this second volume (series), we talk about Pythagoras' Theorem, Elementary Number Theory, Group, Ring, Field, and Fermat's Last Theorem.