# Eureka (Gen Hoshino song)

"Eureka" (Japanese pronunciation:) is a song by Japanese singer-songwriter and musician Gen Hoshino. It was released by Speedstar Records as a digital-only single on January 28, 2025. As the theme song for the medical drama Diary of a Surgical Resident: Madoka  [ja] (2025), Hoshino wrote and produced the track, which takes inspiration from the quiet storm genre and was composed largely within a day. A J-pop and soul ballad with simplistic progression, "Eureka" is about romance and city life. Hoshino sings about his lack of hope despite his despair, and he concludes that uncertainty should be used as a foothold to move forward.
Music critics in Japan generally praised "Eureka" for its lyrics and their application to modern life. A few reviewers also enjoyed the song's composition, which some found simple but detailed. Commercially, the single reached number 11 on the weekly Billboard Japan Hot 100 and number 33 on the Oricon Combined Singles Chart. The song's music video is composed of scenes of Hoshino through a one-week period. It was directed by cover art photographer Kotori Kawashima [ja] and features a cameo from actor Taiga Nakano.

## Writing

As the theme song for the medical drama Diary of a Surgical Resident: Madoka  [ja] (2025), Gen Hoshino began composing "Eureka" using digital audio workstations in late 2024. During production, the song carried the working title "Mountain" in reference to mountain ranges, which had inspired its soundscape. Hoshino conceived "Eureka" as a quiet storm-styled track—slow and mellow, influenced by genres such as soul and jazz. The intro, first verse, chorus, and the arrangement of various instruments were completed within a single day; according to Hoshino, the final track remains largely unchanged from this initial version.
Hoshino described the approach for song's lyrics, which were written shortly after the New Year, as opposite to the process of his 2022 single "Comedy". On "Comedy", a self-imposed rule prohibited Hoshino from writing about himself, but "Eureka" was envisioned as a more personal song. He searched for similarities between his own philosophy and Surgical Resident: Madoka, and he remarked on the song's background in a press comment. He recalled that when he was 26-years-old (the same age as the drama's protagonist), he had written a lyric that contained the word wakaranai (わからない, lit. 'I don't understand'). Retrospectively, he thought that he never had a moment of understanding/eureka.

## Composition

"Eureka" is 3 minutes and 31 seconds long. Hoshino produced and programmed the song, and plays bass and synthesizer; Shun Ishiwaka performs on drums and shaker, Hirotaka Sakurada plays standard and digital piano, and Ryosuke Nagaoka features on electric guitar. Hoshino handled recording with Shojiro Watanabe and Shu Saida. Watanabe mixed the song, while Takahiro Uchida mastered it.
Rockin'On Japan's Koike Hirokazu characterized "Eureka" as a pop song, while Ryūtarō Amano at Mikiki called its middle-tempo soul sound in line with Hoshino's past works like "Comedy", "Ain't Nobody Know" (2019), "Fushigi" (2021), and "Why" (2023). A simplistic ballad without bold progression, "Eureka" is opened by Ishiwaka's shaker, which is accompanied by piano and drums starting with the first verse. Synthesizer and guitar are featured in the first chorus, where Hoshino's vocals are doubled and the polyphonic background vocals layered. The melody is led by the fusion-styled synth in the aftermath of the chorus, and the bass plays in the background throughout the song. Amano noted influences of quiet storm on the track; he compared its progression to the style of Grover Washington Jr.'s "Just the Two of Us" (1980), and its implementation of a shaker to Sade's "The Sweetest Taboo" (1985). Amano also noted similarities to city pop and album-oriented rock, and influences from Haruomi Hosono on Hoshino's bass.
The lyrics on "Eureka" are about city life and adult romance. Hoshino repeats lines concerning the unknown, and the title eureka is used as a negative (to not be discovered). He sings about his lack of hope despite the existence of despair, and questions what can be found in a world without hope. Since he has continued to live, he concludes that hope is unnecessary and that uncertainty should be used as a foothold to move forward. Hoshino sings "The 'present' carries the past and future", and reflects on anxiety and emptiness in lines such as "I bested my sorrows / The fact I'm still breathing / Is proof of that".

## Release and promotion

"Eureka" was first previewed in the first episode of Diary of a Surgical Resident: Madoka on January 14, 2025, before Speedstar Records released the song as a single for download and streaming on Hoshino's 44th birthday, January 28. The song's release was promoted with a teaser—a ten-second video clip posted to social media the morning before the premiere of Surgical Resident: Madoka, which featured the text "Gen Hoshino Eureka", played over by what Sports Bull writers called the percussive sound of maracas. The single's cover art, photographed by Kotori Kawashima [ja] and designed by Hiromi Fujita, depicts Hoshino covered by sunlight as he looks towards the sky. A phone wallpaper and messaging app stickers based on the artwork were awarded to users who pre-saved the song on streaming platforms.
Kawashima directed and filmed the "Eureka" music video, which was premiered to YouTube on January 31, 2025. Hoshino invited Kawashima to his studio during the writing of the song; some scenes were filmed there, while others were taken outside over a one-week time span. A cameo appearance is made by actor Taiga Nakano, who meets with Hoshino over a cup of coffee. A behind-the-scenes video, directed and filmed by Koe Inc.'s Yosuke Yamaguchi, was released on March 5, 2025.
Hoshino first performed "Eureka" for a two-hour special of CDTV Live! Live! on February 10, 2025. A live minimalistic performance of the song subtitled "808 Sessions"—featuring only Hoshino's soul vocals and digital piano by Hirotaka Sakurada—was uploaded on February 26. It was filmed at Hoshino's home studio 808, where the song and most of his upcoming sixth album were also recorded.

## Reception

Japanese music critics praised "Eureka" for its lyrics; some reviewers particularly scored their relevance to modern life. Writing for Rockin'On Japan, Hirokazu called "Eureka" a heart-warming song in contrast to the modern "storm of anxiety", and found the lyrics to almost inventively express overlookable truths. In Mikiki, Amano called the song's focus on darkness and despair a grounded form of realism; in comparison to "delusional hope", he found this more relevant to the modern way of living in Japan, or the world as a whole. Musically, Suzie Suzuki for Yahoo News Japan described "Eureka" as "pleasant" and "fresh". Amano considered the song a win for fans of Hoshino's musical transition towards middle-tempo soul, though he felt "Eureka" took an approach calmer than some of its preceding works. He found that the sound—a combination of a repeated beat, restrained vocals, and unglamorous progression—resulted in an "intimate" mood of city and night. Hirokazu and Real Sound's Tomoyuki Mori considered the composition simple, but enjoyed Hoshino's attention to detail.
In its week of release, "Eureka" earned 9,440 paid digital downloads according to Billboard Japan, and 2,686,567 streams according to Oricon. The song entered at number 11 on the Billboard Japan Hot 100 dated February 5, 2025, and at number 33 on the Oricon Combined Singles Chart dated February 10. The track reached numbers 4 and 44 on Billboard Japan's download and streaming sub-charts, respectively.

## Credits and personnel

Music credits adapted from "Eureka" on Hoshino's official website; visual personnel taken from video description on YouTube

### Music and production

* Gen Hoshino – lead vocals, background vocals, bass, synthesizer, songwriting, production, arrangement, arrangement of choral vocals, programming, recording
* Shun Ishiwaka – drums, shaker
* Hirotaka Sakurada – piano, digital piano
* Ryosuke Nagaoka – electric guitar
* Shojiro Watanabe – recording, mixing
* Shu Saida – recording
* Takahiro Uchida – mastering

### Music video

* Kotori Kawashima [ja] – direction, videography, editing
* Shintaro Tamada – assistant direction, editing
* Yohei Kawada – creative direction, production
* Jin Otabe – assistant production
* Yosuke Yamaguchi (Koe Inc.) – behind-the-scenes videography
* Ryotaro Takahashi – online editing
* Matawe Wongpuak – online editing
* Tomokazu Saito – multi-audio engineer
* Hiromi Fujita – title design
* Dai Ishii – styling
* Shuto Sugiyama – assistant styling
* Rumi Hirose – hair-styling
* Miyuu Takeuchi – hair-styling
* Masaki Takahashi – hair-styling for Taiga
* Gen Hoshino – cast
* Taiga Nakano – cameo

## Charts

Weekly chart performance for "Eureka" (2025) :
| Chart (2025) | Peak position |
| Japan (Billboard Japan Hot 100) | 11 |
| Japanese Combined (Oricon) | 33 |