| Isshun | |
| Cover: | Isshun.png |
| Type: | Single |
| Artist: | Shizuka Kudo |
| Label: | Pony Canyon |
| Prev Title: | Kirara |
| Prev Year: | 1998 |
| Next Title: | Akashiya Sanma-san ni Kiite Minai to ne |
| Next Year: | 1999 |
is a song recorded by Japanese singer Shizuka Kudo. It was released as a single by Pony Canyon on November 6, 1998. The song served as theme song to the EX morning show Yajiuma Wide.[1] It made its first album appearance on the compilation album, Millennium Best.
"Isshun" was written by Luna Sea lead vocalist, Ryuichi Kawamura, under the pseudonym ЯK.[2] It is the second consecutive single written by Kawamura. Kudo and Kawamura had been working on an album that would be entirely produced by Kawamura, but ultimately the project was shelved. The song is composed in the key of G-sharp major and Kudo's vocals span from G3 to C5. Lyrically, the song describes the moment one falls in love. Kudo described her own vocal performance on the track as reminiscent of her old singing style.
The single debuted at number 29 on the Oricon Singles Chart, selling 11,000 copies in its first week.[3] It fell ten positions to number 39 the following week, recording sales of 7,000 copies.[3] "Isshun" charted a total of four weeks in the top 100.[4]