Hatsune Miku: Colorful Stage!, known in Asia as Project Sekai: Colorful Stage! feat. Hatsune Miku (Japanese: プロジェクトセカイ カラフルステージ! feat.初音ミク, Hepburn: Purojekuto Sekai Karafuru Sutēji! fīcharingu Hatsune Miku), is a Japanese mobile rhythm game developed by Colorful Palette, a studio of CyberAgent's Craft Egg, and published by Sega Corporation. The game is a spin-off from Sega's Hatsune Miku: Project DIVA series, and features the Crypton Future Media's virtual singers Hatsune Miku, Megurine Luka, Kagamine Rin and Len, Meiko, and Kaito, alongside the cast of 20 original human characters that are split into five units, each with a unique theme. Set in the real world where Virtual Singers only exist as fiction, the characters come across another world called "Sekai," where various "true feelings" are projected. The game was released for Android and Apple devices on September 30, 2020. It was developed with Unity, and uses the Piapro Studio NT engine for voice synthesis.
Hatsune Miku: Colorful Stage is set in the real world, specifically in the city of Tokyo and Yokohama (both located in the Greater Tokyo Area and the Kantō region). In this game, Hatsune Miku and her friends are famous fictional singers existing in the real world as Virtual Singer. They sing songs from creators all over the world, but they also exist in "Sekai," (セカイ) a mysterious world different from the real world that is created from a person's "true feelings", featuring various visual appearances based on the person. There are as many Sekai as there are emotions, and its form changes depending on the person's emotions. Therefore, the focus of the game is on the original characters and their journeys to find their "true feelings" with the help of the Virtual Singers.
In order to enter Sekai, one must find and play the song "Untitled." This silent song has no melody or lyrics and is created at the same time as the Sekai, and is mysteriously inserted on their devices. It can be anything, such as a game console, a smartphone, a smartwatch, a TV, a tablet, and a computer. When they play an "Untitled" song, they can travel between the real world and the Sekai. As one is able to discover their true feelings, the song will contain a playable melody and lyrics, and well as its title.