A famous Japanese musician who was involved in composing music for the opening ceremony of the upcoming Tokyo Olympics has quit after admitting to "inhuman" sexual abuse of disabled children as a schoolboy.

Keigo Oyamada, 52, who is known in Japan as Cornelius, resigned in disgrace days after an interview he gave in the 1990s -- in which he bragged to local news media that he forced a disabled boy to masturbate in front of others and to eat his own faeces -- resurfaced soon after his name was announced as composer of the opening ceremony.

Keigo Oyamada

He has since apologised for his conduct as a student and said he was very "immature" when he preyed on his classmates.

The revelation about his 1990s interview and the response to it by some of his victims became viral on social media sites in Japan. Initially, the organising committee of the Tokyo 2020 Olympic Committee had sidelined him but later decided to remove his work altogether from the ceremony.

Oyamada is best known in Japan as one of the originators of the kitschy Shibuya-Kei sound, which drew heavily on American pop music from the 1960s produced by the likes of Burt Bacharach and Phil Spector.