Eureka (Sakanaction song)

"Eureka" (Japanese: ユリイカ, Hepburn: Yurīka; IPA: [jɯɾiꜜːka]) is a song by Japanese band Sakanaction from their seventh studio album, 834.194 (2019). It was released as a single in January 2014, as a double A-side single with the song "Good-Bye". The minimal techno and city pop song served as the ending credits theme song of the film Judge! (2014), while their 2010 single "Identity" was used as the film's theme song. The song was composed while the band's vocalist and songwriter Ichiro Yamaguchi was physically and mentally unwell. He used his feelings of homesickness during this time to write lyrics that compared his current residence, Tokyo, to his hometown of Otaru, Hokkaido.

The physical single debuted at number two on Oricon's weekly singles chart, while "Eureka" reached number four on the Billboard Japan Hot 100, less successful than "Good-Bye" which reached number two. Critics praised the song's "addictive" electro and minimalist sound, and felt that it was reminiscent of the works of Rei Harakami.