"Eureka" (Japanese: ユリイカ Hepburn: Yurīka) (Japanese pronunciation: [yɯɺi:ka]) is a song by Japanese band Sakanaction. 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.