Rei Kiriyama (桐山 零 Kiriyama Rei) is the main protagonist of the series. He is a 17 year old 5 dan in Shogi, who became a professional during middle school.
Rei has had a very traumatic background. He mentions he was bullied at school and in the neighborhood, and couldn't relate to the other children. After his parents and sister died in a traffic accident, he was taken care of by his father's friend Kōda and became his apprentice in shōgi. Through his step-father's tutelage, he became a professional shōgi player after completing middle school. Afterwards, he decided leave home, due to feeling guilty about his presence negatively affecting his foster family. After moving out, he starts living alone in an apartment at the city of Rokugatsu-chō. However, experiencing a desire to attend school, Rei later joined a high school after a one-year delay.
As a result of his traumatic childhood, Rei is socially reclusive and has many emotional scars that still plague him to his day. In everyday conversion, he is meek and shy, even speaking in keigo to those younger than him.