Yamakawa was not happy with the offer the Seibu Lions gave him during contract negotiations on December 5, 2017. He decided not to sign and became the first Lions holdover since 2010. Yamakawa earned an estimated sixteen million yen this season. The Lions may have offered around thirty million yen. Yamakawa may have wanted something in the range of forty million yen.
Yamakawa studied Japanese calligraphy when he was a child — from kindergarten until he was about fifteen. He made it to 8-dan before quitting.
Source: Sponichi 8/29/2017
Yamakawa filed marriage papers with a twenty-seven-year-old woman, who was one-year ahead of him at Fuji University, on August 9, 2017. The two celebrated their seventh year together on August 9.