The Sunflower on the Shogi Board (Banjo no Himawari)

In 1994, a human skeleton is found in the mountain of Saitama. A shogi game piece is found with the skeleton. The shogi piece was made by a master craftsman. Veteran detective Takeshi and rookie detective Naoya begin to investigate the owner of the shogi piece. Keisuke is a genius professional shogi player. While doing an interview with a shogi magazine, Keisuke recalls his childhood. In 1972, Keisuke was an elementary school student and he lived with his father. His father was violent and did not even give Keisuke a proper meal. Keisuke happened to meet Koichiro, who was a retired teacher. Koichiro was nice to Keisuke and, because of him, Keisuke became fascinated with the game of shogi. Detective Takeshi and Detective Naoya go to see Keisuke. Is Keisuke the killer? Who is the dead person?