Sorayama was born the eldest son of a carpenter in 1947, Ehime Prefecture, Japan. He entered Shikoku Gakuin University in 1965. After the publication of Pink Journal in 1967, he left the school and entered the Chuo Art School. Graduating in 1969, he was hired by an advertising firm as a comprehensive illustrator. He began working independently as a free-lance illustrator in 1972.