Shusaku (本因坊秀策, Yasuda Eisai, Kuwahara Shusaku, Invincible Shusaku, born Kuwabara Torajiro (桑原虎次郎); June 6, 1829 – September 3, 1862) was a Japanese professional Go player during the 19th century. He is known for his undefeated streak of 19-games during the annual castle games; his thirty-game match with Ota Yuzo; the eponymous Shusaku opening; and his posthumous veneration as a "Go sage". Next to his teacher, Hon'inbō Shūwa, he is considered to have been the strongest player from 1847/8 to his death in 1862. He was nicknamed Invincible Shusaku because of his castle games performance.