Maruyama was involved in the establishment of MADHOUSE in 1972. Since then, he has nurtured talents such as Tetsuro Araki, Atsuko Ishizuka and the late Satoshi Kon. Among the anime works he has produced are Unico, Ninja Scroll, Card Captor Sakura, Monster, Death Note, The Girl Who Leapt Through Time, Paprika, Redline and Supernatural: The Animation. In 2011, Maruyama left MADHOUSE and formed MAPPA, whose first major project was 2012's Kids on the Slope television anime series.
His recent works involve Punch Line, Rage of Bahamut, Ushio To Tora, and of course Japan’s award winning and record-breaking crowdfunded film In This Corner of the World.