|This article is about a/an set of devices in Kamen Rider Fourze.|
A Zodiarts Switch (ゾディアーツスイッチ Zodiātsu Suitchi) is a device which is activated by a person, from then on known as a Switcher (スイッチャー Suitchā), to become a monstrous construct known as a Zodiarts. From there, a Zodiarts Switch gathers a mysterious energy from space called Cosmic Energy (コズミックエナジー Kozumikku Enajī) that forms a monstrous construct around a human that can withstand transwarp travel. These switches are provided by Mituaki Gamou to Amanogawa High students as they appear to have the potential to evolve the Zodiarts Switches' powers by their state of minds. A Zodiarts Switch imprints on its Switcher, as once a switch is activated, the only person who can use the switch is the Switcher himself.
Exceptions only occur to very few who has a special constitution allowing use of other Zodiarts' switches. The only such exceptions revealed thus far are Mitsuaki Gamou and Kou Tatsugami. A Zodiarts Switch can only be activated by a person with negative intentions and is impossible to be truly used for good. According to Tachibana, one has a higher chance of finding a lost artificial satellite in the entire universe than finding a Zodiarts Switcher that truly uses his or her powers for good. Though given the fact that Tachibana's true identity is that of Professor Kuniteru Emoto, who is himself the Virgo Zodiarts and who dedicates his life to undermine Gamou's plan for good causes, and to a lesser extent, Tachibana himself, the "evil" nature of the Zodiarts Switches is questionable.
It is also stated that Zodiarts Switches take a physical toll on the user as a consequence of the forced evolution, causing the longest-term users to dissolve into stardust after being defeated by a Limit Break rather than simply switching off. In some shorter-term cases the user's powers can backfire on them after defeat if they were overused, as in the case of the Aries Zodiarts.
Compatibility is another important and dangerous feature of the Zodiarts Switch. If activated by an incompatible user, it backfires on them, such as in the case of Jiro Iseki, who is rendered comatose after activating an incompatible switch. Conversely, a Zodiarts Switch will reach the Last One (ラーストウァン Rāsuto Wan) state when the user is overwhelmed by their negative emotions to the point that they no longer wish to be human, with the switch announcing "Last One" in the voice of the Horoscopes who provided the Switch. A Last One Switch also changes its appearance, growing spikes and an eyeball-like structure, as well as changing the position of the button.
When the Switcher activates the Switch at this point, the transformation becomes irreversible as the Switch drains its Switcher of their conscious mind and uses it to become a Zodiarts permanently. The Switcher's empty body is ejected from the Zodiarts, covered in a cobweb-like substance. In this state, the Zodiarts becomes extremely powerful and can only be defeated if targeted at point of its body where the Zodiarts Switch is located.
In some cases, the Last One state doubles as a pupa state where certain Zodiarts can evolve further into one of the Horoscopes once the Resurrection Star (最輝星 Saikisei, lit. "Brightest Star") on its body begins to glow, absorbing their original bodies to remain human. Should a person have latent exceptional compatibility with a Horoscopes Switch, a regular Zodiarts Switch might evolve into a Horoscopes Switch the very first time it is activated, allowing its Switcher to skip the Last One state altogether and instantly become a Horoscopes-type Zodiarts.
Fighting a Zodiarts in its Last One state, a Kamen Rider can use one of its Limit Break (リミットブレイク Rimitto Bureiku) finishing attacks to destroy the monster's body and get the Zodiarts Switch. Once properly switched off, the Zodiarts Switch will vanish into a singularity, returning the user's mind to its body. However, once an authentic Zodiarts Switch becomes an authentic Horoscopes Switch, practically nothing can destroy it.