COSMONAUTS was YZYX's 7th VOCALOID work and an official demo for VY1v4. The song is a multilingual Electro song that showcases VOCALOID4's new features. The lyrics basically makes an analogy between the music and cosmos, and calls to the listener to explore the new musical boundaries. Like other VY1v4 demos, the song became unavailable for few days, due Yamaha requested to the authors put their works on hold until the release of VOCALOID4.