In 1997, he released the album Fantasma, which landed him praise from American music critics, who called him a "modern-day Brian Wilson" or the "Japanese Beck".

His first claim to fame was as a member of the pop duo Flipper's Guitar, one of the key groups of the Tokyo Shibuya-kei scene.

[3] In 2006 and 2007 respectively, the song "The Micro Disneycal World Tour" from the Fantasma album, was used for Nick Park's Creature Comforts and Sky television's "Surf, Speak, See" advertisements in the UK.

It had also been used several years earlier in an ironic NFL television commercial in the US, which juxtaposed the song's relaxing qualities with video clips showing rapid, aggressive football playmaking.

[5] The music of Cornelius could be described as experimental and exploratory, and often incorporates dissonant elements alongside more familiar harmonically "pleasing" sounds.

[citation needed] Oyamada married musician and collaborator Takako Minekawa in 2000 and they have one child, Milo, named after the son of Cornelius in Planet of the Apes.

[18] On the same day, the TOCOG issued a statement stating they were unaware of the interviews[19] and that while Oyamada's actions were "very inappropriate", they had not dismissed him from the ceremony.