Sonyu was the son of Sanemon, who ran a draper’s shop Kariganeya, and was adopted by Ichinyu at the age of 2. He eventually married Ichinyu’s daughter (Ozu). His original name was Heishiro, and he was later renamed Sokichi. Ogata Korin and Ogata Kenzan were his cousins, and his great-grandmother was Honami Koetsu’s sister. Ichigen was his brother-in-law who was 2 years older, and Sonyu took over as the head of the family at age 28, retired at age 45, and passed away at age 53. Between 1688 and 1695, he wrote “Sonyu Monjo,” which contained 2 sets of notes on the Raku family and 1 family tree of the Raku family, with his father Ichinyu. This is the oldest written document on the lineage of the Raku family. Sonyu succeeds Ichinyu as the head of the family around 1691, but 100 years had already passed since the passing of Chojiro.