teamOS is a circle consisting mainly of the composers Hitoshizuku-P and Yama△, whom are collectively known as Yamashizuku. Some of their most popular songs include "Himitsu ~Kuro no Chikai~", "Karakuri卍Burst" and "Bad ∞ End ∞ Night". Their music style consists mostly of fantasy-esque songs. In addition, light novels based on the Himitsu Series, Karakuri Series and Night ∞ Series have been released so far.