[ja], it is a jazz and soul-influenced track inspired by the things Hoshino did not understand when he was 26-years-old, the same age as the show's protagonist.

On January 8, 2025, it was announced that Gen Hoshino would perform "Eureka", the theme song to the TBS Television medical drama Madoka 26-sai, Kenshū-i Yattemasu!  [ja].

[1] Written, produced, and arranged by Hoshino, outlets reported that the song has the essences of his musical "roots" in jazz and soul.

[3][5] A teaser for the song's music video, starring Hoshino and directed by Kotori Kawashima, was published alongside the announcement.

To promote the release, Hoshino's label announced campaigns awarding a phone wallpaper and stickers based on the cover art to users who pre-save or download the song.