心世紀 (Shinseiki) and 罪十罰 (Tsumitobatsu) just released 瑠璃ノ誓 (Ruri no Chikai) — streamed under the English title Azure Oath — as the six-member anthem for 少女革命計画 (Girls Revolution Project), KAMITSUBAKI STUDIO’s music x story label. It lands right as the two units head into their second-anniversary live, and the song plays like a vow renewed rather than a first promise.
Who Are Shinseiki and Tsumitobatsu?
Girls Revolution Project is built around two units. Shinseiki — 御莉姫 (Orihime), 佳鏡院 (Kakyoin), and 硝子宮 (Garasumiya) — is billed as an “Xtuber” unit that crosses between virtual and real performance. Tsumitobatsu — 氷夏至 (Hinageshi), 美古途 (Mikoto), and 夕凪機 (Yunagi) — is the project’s virtual singer unit, built around a darker, more agitated sound. The two debuted together in August 2024 at KAMITSUBAKI FES, and every full-group track since has functioned as a checkpoint in their shared story — this one arrives as they head into their 2nd LIVE, “Revolutio,” celebrating two years since that debut.
The Sound and Feel of “Ruri no Chikai”
Where the project’s collaborative tracks have leaned into ballad territory before, Ruri no Chikai pulls in live strings — 河合晃太 plays violin and viola over 水野谷怜‘s programming and arrangement, giving the track a cinematic backbone that sits somewhere between orchestral pop and the kind of sweeping theme song you’d expect from an anime finale. The title itself, “azure oath,” sets the emotional register before a single lyric lands — this isn’t a song about doubt or conflict, it’s about a promise renewed.
Six Voices, One Story
What makes these full-unit collaborations distinct from either group’s solo output is how differently Shinseiki and Tsumitobatsu are built to sound — one project leaning toward performance-forward pop, the other toward moodier, more theatrical singing — and this track is where those two textures have to fold into a single line. 真崎エリカ‘s lyrics carry the six of them through shared verses rather than splitting the song into solo spotlights, which fits the anniversary framing: this is a song about the group as a whole, not a showcase for any one member.
The Visual World Built Around It
The MV, directed by Yazhirushi, pairs illustration work from 咲の字。 and 米室 with graphic design from .MP. Girls Revolution Project has always treated its videos as extensions of the project’s ongoing “story” side rather than standalone visuals, and the character designs across both units originate from PALOW., giving the whole label a consistent visual identity even as different artists rotate through individual releases.
Why This Release Matters Right Now
Two years in, Girls Revolution Project has built out a real discography — full-unit tracks, unit-specific singles, even a cover EP — and a live history that started with a sold-out debut show in Kawasaki last year. Ruri no Chikai arriving ahead of the 2nd LIVE “Revolutio” in Shibuya isn’t a coincidence; it’s the project doing what it’s done at every major checkpoint so far, using a new song to mark the moment before the show does the rest.
Track Credits
- Title: 瑠璃ノ誓 (Ruri no Chikai / “Azure Oath”)
- Vocals: 心世紀 (Shinseiki) × 罪十罰 (Tsumitobatsu)
- Lyrics: 真崎エリカ (Masaki Erika)
- Composition & Arrangement: 水野谷怜 (Mizunoya Rei)
- Violin, Viola: 河合晃太 (Kawai Kota)
- All Other Instruments & Programming: 水野谷怜 (Mizunoya Rei)
- Vocals Recording Engineer: 山重拓太郎 (Yamashige Takutaro)
- Mixing Engineer: 住野雄飛 (Sumino Yuto)
- MV Director: Yazhirushi
- Illustration: 咲の字。, 米室
- Graphic Design: .MP
- Label: KAMITSUBAKI STUDIO / 少女革命計画 (Girls Revolution Project)
- Released: August 12, 2026
▶ Watch: Shinseiki x Tsumitobatsu — Ruri no Chikai (Azure Oath) (Official MV) on YouTube
