At first, he was working for a bookbinder. In 1980, he made his official debut as a manga artist in Ribon no Kishi. Maruo was a frequent contributor to the legendary underground manga magazine Garo. Though most prominently known for his work as a manga artist, Maruo has also produced illustrations for concert posters, CD Jackets, magazines, novels, and various other media. Some of his characters have been made into figures as well.