The Henshin Onsa (変身音叉, Henshin Onsa lit. "Transformation Tuning Fork") is a transformation device resembling a tuning fork. It is the most commonly used transformation device among the Oni Kamen Riders of the organization Takeshi, usually those whose arsenal revolves around the percussion. It is said to be the simplest of all transformation devices to make, yet has the capability to unlock the greatest power within all Oni that use it. It has two forms: 'cellphone mode' and 'tuning fork mode'.