Overview
セカイ is a cross-media anthem that originated as the theme song for the mobile rhythm game Project SEKAI Colorful Stage! feat. Hatsune Miku, written as a collaborative composition between two towering figures in the VOCALOID and doujin music scenes: DECO*27 and Shouta Horie (kemu, of「六兆年と一夜物語」fame). The track was composed by Horie, arranged by Rockwell, and features lyrics by DECO*27. While the original version (used in CHUNITHM) is a solo Hatsune Miku performance, the version ported to maimai, dubbed the "Sekai version", expands the vocal lineup to include Ichika Hoshino (CV: Ruriko Noguchi), Tsukasa Tenma (CV: Daisuke Hirose), and Kanade Yoisaki (CV: Tomori Kusunoki) alongside Miku, each character representing a different in-game unit from Project SEKAI. In maimai, the song uses a shortened 1:48 edit tailored for arcade play.
Videos
Charts
DX
BASIC
2(2)
102 notesDesigner: -|Tap 82Hold 4Slide 4Touch 8Break 4
ADVANCED
6(6)
211 notesDesigner: -|Tap 170Hold 10Slide 6Touch 21Break 4
EXPERT
10(10)
360 notesDesigner: 小鳥遊さん|Tap 254Hold 39Slide 33Touch 16Break 18
MASTER
12+(12.8)
553 notesDesigner: うさぎランドリー|Tap 402Hold 41Slide 34Touch 46Break 30
Trivia
- セカイ is the theme song for Project SEKAI Colorful Stage! feat. Hatsune Miku, a mobile rhythm game that blends original characters with classic VOCALOID songs.
- The composition credits are split: Shouta Horie (kemu) composed the music, Rockwell handled the arrangement, and DECO*27 wrote the lyrics.
- The title セカイ (Sekai) means 'world' in Japanese, referencing the in-game 'Sekai', virtual worlds born from characters' feelings where they meet Miku.
- maimai uses the 'Sekai version' with vocalists from three different Project SEKAI units: Leo/need (Ichika Hoshino), Wonderlands×Showtime (Tsukasa Tenma), and 25-ji, Nightcord de. (Kanade Yoisaki).
- The song was added to maimai でらっくす FESTiVAL on October 7, 2022 in Japan. In the Asian region it launched a year later on October 6, 2023 with FESTiVAL PLUS, and in China it was added to 舞萌DX 2025 on December 4, 2025.
- The MASTER chart (level 12+, constant 12.8) was designed by うさぎランドリー (Usagi Laundry), who is also known for designing this song's ONGEKI charts. The EXPERT chart (level 10) was designed by 小鳥遊さん (Takanashi-san).
- The song also appears in CHUNITHM (original Miku-only version) and ONGEKI (Sekai version), making it one of a handful of songs that appear across all three of Sega's major arcade rhythm game series.
- The MASTER chart features 553 total notes with a balanced mix of all note types: 402 Taps, 41 Holds, 34 Slides, 46 Touches, and 30 Breaks, giving it a dense but approachable feel for a 12+.
FAQ
- Who composed the song セカイ?
- セカイ was composed by Shouta Horie (kemu), with arrangement by Rockwell and lyrics by DECO*27. It was released as a collaboration between DECO*27 and kemu for Project SEKAI Colorful Stage! feat. Hatsune Miku.
- What version of maimai added セカイ?
- セカイ was added to maimai でらっくす FESTiVAL on October 7, 2022. It later arrived in the Asian version with FESTiVAL PLUS (October 6, 2023) and in the Chinese version with 舞萌DX 2025 (December 4, 2025).
- What is the difference between the original version and the Sekai version of セカイ?
- The original version used in CHUNITHM features only Hatsune Miku on vocals. The 'Sekai version' used in maimai and ONGEKI adds three Project SEKAI characters, Ichika Hoshino, Tsukasa Tenma, and Kanade Yoisaki, alongside Miku. The maimai version is also a shortened 1:48 edit.
- What difficulty level is the MASTER chart of セカイ in maimai?
- The MASTER chart is level 12+ with a difficulty constant of 12.8. It was designed by うさぎランドリー (Usagi Laundry) and contains 553 total notes across all note types.
- Who designed the charts for セカイ in maimai?
- The EXPERT chart (level 10) was designed by 小鳥遊さん (Takanashi-san), and the MASTER chart (level 12+) was designed by うさぎランドリー (Usagi Laundry). The Basic and Advanced charts have no credited designer.
- What does the title セカイ mean?
- セカイ (Sekai) means 'world' in Japanese. The title directly references the core concept of Project SEKAI, where virtual worlds called 'Sekai' are born from characters' emotions and serve as meeting places with Hatsune Miku.
