A Zodiarts is a monstrous construct that is produced when a Zodiarts Switch is activated by a person, then on known as a Switcher. Each of the Zodiarts are named after one of the Western constellations. From there, a Zodiarts Switch gathers Cosmic Energy 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 themselves. Exceptions only occur to very few who has a special constitution allowing use of other Zodiarts' switches such as Mituaki 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. 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 Zodiart.
Zodiarts Switch are not compatible to some people. They backfire with incompatible people such as Jiro Iseki, who is rendered comatose after activating an incompatible switch. Conversely, a Zodiarts Switch will reach the "Last One" state when the user is overwhelmed by their negative emotions to the point that they no longer wish to be human. A Last One Switch also changes its appearance, growing spikes and an eyeball-like structure. 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 can only be defeated if targeted 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 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 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.
Toshiya Miura is a second-year student part of AGHS football club who became tired of how the team's members treat him as a mere lowly servant and never let him have a chance on the field. To get back at Shun, he is given a Zodiarts Switch that allows him to become the Orion Zodiarts, a Zodiarts with intense brute strength which is armed with "Lemnos" club and "Chios" shield. Although he is initially defeated by Fourze, the mysterious Scorpion Zodiarts returns the Zodiarts Switch to Miura, allowing him to use it once more to confront Shun. After Tomoko Nozama reveals the identity of the Zodiarts to Gentaro and Yuki, they reach Miura in time to persuade him not to go through with his plans. However, Shun pushes Miura over the edge by kicking him out of the football club, driving him to use his Switch as it enters its Last One state. As the monster has amassed enough energy to blow up the stadium, Kengo directs Fourze to take the Orion Zodiarts into the upper atmosphere in order to destroy him, allowing the Zodiarts Switch to be turned off so Miura's mind can return to his body. Miura was hospitalized soon after. Miura later recovered from the ordeal, but he refused to go back to school and ignored Shun's many apologies. It was later revealed that it was not because he didn't want to go back to school, but he rather was avoiding returning to school grounds due to his new-found addiction to the Cosmic Energy. The Horoscopes use this to their advantage by having Sonoda present him with a new Zodiarts Switch which, due to his emotional state, immediately reaches its Last One state as soon as he grabs hold of it. However, due to Gentaro, his girlfriend Mari and the rest of the KR Club showing him his old self, he is able to reject the Switch of his own free will. Afterwards, he befriends Gentaro and joins the photography club to be with Mari.
Tamae Sakuma is a third-year student cheerleader and one of Miu's "sidekicks". However, Tamae has become tired of Miu's two-year winning streak in the annual Queen Festival, a contest that votes for the "queen" of the student body. To stop Miu from winning her third year so she would be able to win the contest herself, Tamae is given the Zodiarts Switch that allows her to become the Chameleon Zodiarts, a Zodiarts that can appear invisible as well as attack with tongue-like tendrils. To remove Miu from the contest, Tamae begins to attack students that could be potential threats to her success. Then, when Miu takes the stage for the talent competition, Tamae fakes being attacked herself so she would be able to transform and cause a commotion, allowing for a video of Miu lambasting the student body to play. When her identity is revealed, Tamae fakes remorse to catch Miu off guard and injures her severely to remove her from the contest. However, Miu musters up enough strength to return to school despite her yet-to-recover injuries and wins back the hearts of the student body with a powerful speech. Tamae, enraged that her plan has failed, ignores Kengo's warning against using her Zodiarts Switch when it enters its Last One state. She attacks Miu once more, but Fourze is able to save Miu and eventually destroys the Zodiarts, gaining access to the Zodiarts Switch to shut it off. After Miu wins the contest for the third year in a row, she forgives Tamae for her actions, and renews their friendship under the promise that Tamae would beat Miu through honest means. She is one of the students to constantly being absent from the school because of the Cosmic Energy of the Zodiarts Switches. She returns in episode 25, wanting to ask Gentaro to the prom. She, along with Ritsuko and Jin are accused to be the cause of all havoc wrecked in the school near graduation, irritating them enough to skip their convocation altogether. At Gentaro's annoying insistence, she and Jin end up going to the prom together instead.
Fumihiro Nitta is a first-year student femcer who was used by JK as his human shield from bullies. As a result of injuries from taking the beatings, Nitta was unable to enter a fencing tournament before learning of JK's deception and vowed to take his revenge. The chance for payback on JK presented itself when the Scorpion Zodiarts gives him a Zodiarts Switch that allows him to transform into the Unicorn Zodiarts. While fighting Kamen Rider Fourze, Nitta's desire for revenge causes a sudden evolution in his Zodiarts form where his horse-faced mask converts into the Longsword Monarch rapier. This new power, combined with his ability to project horseshoe-shaped energy projectiles, makes the Unicorn Zodiarts a force to be reckoned with in a fight. After capturing JK, Nitta amusingly allows him a chance for freedom by contacting someone for help, with full knowledge that no one in JK's circle would save him. However, Gentaro, thought to be the last on the list who'd actually come save JK, proves Nitta wrong by coming to save the guy who betrayed his trust. Gentaro manages to transform into Kamen Rider Fourze Elek States and destroys the Zodiarts. Though JK intends to beat the daylights out of Nitta for slighting him, Gentaro stops him while reminding him that he is the one in the wrong in the first place, while offering his friendship to Nitta.
Teruhiko Satake is a first-year student who is the rebellious son of AGHS's Takashi Satake. Though he is a student who scores good grades, he is unhappy with his life and adopts delinquent hobbies and mannerisms. At some point, he receives a Zodiarts Switch from the Scorpion Zodiarts in order to transform into the Hound Zodiarts and uses his newly gained abilities to be himself and go on a rampage, or "hunting" as he calls it, attacking anyone and anything nearby when he feels like it. He fights with his powerful claws and the chain that hangs around his neck. The Hound Zodiarts can also fire a barrage of needle-like energy bullets from the dog's face on his chest. Eventually in his Last One state, the Hound Zodiarts gains a thickened hide and none of the usual attacks from the Kamen Rider work on him. While the Scorpion Zodiarts supports the Hound Zodiarts in fighting Fourze, Shun Daimonji pilots the Powerdizer to hold the former off so the Kamen Rider can fight the Hound Zodiarts one-on-one and destroy him.
Ritsuko Usaka is a third-year girl who has been blamed for various unexplained incidents in Amanogawa High due to her tendency to isolate herself and have certain psychic powers, much like Tomoko. She gives into the persecution and becomes the bad girl everyone perceives her to be as she forms her own witches' coven called the Lunar Witches with other scorned social outcasts. She is given a Zodiarts Switch that allows her to transform into the Altar Zodiarts, granting her powerful telekinetic powers via her Aradia staff. However, Ritsuko's passion for the occult evolves her Zodiarts form to also use pyrokinetic powers. Creating moon pendants for her followers to wear, Ritsuko uses her powers to make it appear that she and the members of her group are actually witches before Kengo exposes the deception. By then, using the Zodiarts Switch in its Last One state, the Altar Zodiarts proceeds to enact her plan to burn the entire school to the ground. When her plan is ruined, she becomes infuriated and overpowers Kamen Rider Fourze in battle. Upon transforming into Fire States, Fourze absorbs her fire-based attacks before destroying her Zodiarts form. She returns in episode 25, wanting to ask Gentaro to the prom. She, along with Tamae and Jin are accused to be the cause of all havoc wrecked in the school near graduation, irritating them enough to skip their convocation altogether. To ensure that prom goes well for everybody, the Kamen Rider Club have Ryusei be her prom date, which she is satisfied enough to go along with.
Hiroki Makise is a second-year student who is the president of the AGHS astronomy club who is infatuated with Yuki and constantly stalks her. Obtaining a Zodiarts Switch, Makise becomes the Pyxis Zodiarts and uses his dowsing rod-like horns to track down anything and also direct the motion of any object he points them at. In combat, the Pyxis can use the mentioned horns to slash his opponent, though in a very ineffective manner as Makise himself is not a competent fighter. After seeing her with Gentaro, overpowered by Fourze and the Powerdizer in their first fight, a heart-broken Makise decides to make Yuki pay for her choice in friends. To that end, he pretends to help Yuki find the missing locker that connects to the Rabbit Hatch so he can destroy it, succeeding by redirecting the missiles from theLauncher Module. Soon after, Makise decides to exact his revenge on every other girl who rejected him by having them get on a bus which he would force over an unfinished bridge. However, after the Zodiarts Switch assumes the Last One state, the Pyxis' scheme fails when Fourze Elek States uses the Stealth Module to move around unseen, breaking the horns on his arms off with his Billy the Rod while he is at it. Rendered powerless, the Pyxis Zodiarts is quickly destroyed with Makise back in his body as he receives swift and brutal retaliation from the girls.
Soshi Motoyama is a second-year student who is the president of the AGHS art club who wishes to create the perfect piece of art for a local kindergarten, having given them one a year prior. He is approached by the Libra Zodiarts, seeing him as a potential Horoscopes member, and is given a Zodiarts Switch that allows him to transform into the Perseus Zodiarts, arming him with the Oracle sword. He also has Medusa on his left arm, which enables him to turn anything he touches to stone. Motoyama uses his power to attack and petrify anyone and anything that interferes in his work's creation. Even though his Last One form is destroyed by Fourze Fire States, the Switch recreates the Perseus Zodiarts's body as he gains the ability to fire petrification beams from his Medusa hand. However, though Gentaro failed in his attempt to reach him by challenging him to a painting contest, the Perseus later realizes that he made a grave error in judgement over his actions by realizing that the perfection he sought is only in form and was for his own satisfaction only. The Perseus then accepts Gentaro's friendship with the intent of returning to a human before the Libra Zodiarts converts him into a berserker for his Resurrection Star losing its glow. However, with the help of Kamen Rider Meteor holding the Libra Zodiarts at bay, Kamen Rider Fourze uses the Pen Switch to disable the berserk Perseus before destroying him. Back in his body, Motoyama is later seen creating a new painting to give to the kindergarteners. His Zodiarts form is seen in Ryusei's dream, defeated by Meteor Storm to search for the Aries Zodiarts.
Kimio Nonomura is a second-year student who is Kengo's rival. The Zodiarts Switch given to him by the Libra Zodiarts enables him to transform into the Lynx Zodiarts who is agile and has sharp claws on both of his hands. Due to the infighting between Kamen Riders Fourze and Meteor, the latter manages to destroy the Lynx Zodiarts with the Starlight Shower. However, the Lynx Zodiarts revives and enters the stage of potential that will enable him to transform into one of the Horoscopes, with Kamen Rider Meteor covering the Zodiarts's escape on the hope that the Lynx Zodiarts might evolve into the Aries Zodiarts. He continues his attacks until he is pursued by Kamen Rider Fourze using the Wheel Switch, then is promptly destroyed by Fourze using the Rider Lightning Drill Kick and his Zodiarts Switch is turned off. His Zodiarts form is seen in Ryusei's dream, defeated by Kamen Rider Meteor Storm in search of the Aries Zodiarts.
Jin Nomoto is a third-year student who is the intimidating captain of the AGHS track and field team who forbids his team from taking outside help to secure his control over his teammates. He receives a Zodiarts Switch from the Libra Zodiarts and is able to become the Dragon Zodiarts. His nigh-impervious hide makes him immune to physical attacks and resistant to heat and electrical energy, and he is able to absorb and redirect energies, as well as create metal spheres to punch with or throw. He is sent by the Libra Zodiarts to get rid of Fourze and Meteor, and he sees it as nothing more than a fun challenge. He is also deemed by the Virgo Zodiarts to be on par with a Horoscopes member in terms of power, making him an ideal Horoscopes member. An important clue to the Dragon's identity was that he would not stop talking about how fighting the Kamen Riders is more fun than track practice. Jin reveals himself to be the Dragon in front of everyone after seeing that Kengo continues to help Rumi Egawa. After entering the Last One state, the Dragon is compressed into oblivion by Kamen Rider Fourze with the Switch switched off and Jin taken to the hospital soon after. He is seen later appreciating Gentaro's efforts in changing him though chides him for being oblivious to Tamae's and Ritsuko's feelings, both who wanted to go the prom with Gentaro. He, along with Tamae and Ritsuko are accused to be the cause of all havoc wrecked in the school near graduation, irritating them enough to skip their convocation altogether. He went to prom with Tamae eventually due to Gentaro's annoying insistence.
Natsuji Kijima finds a Zodiarts Switch that has been kicked out of the Libra Zodiarts's hand while he was attacked by Kamen Rider Fourze. He then uses it to become the Pegasus Zodiarts and enacts a revenge scheme on the new class 2-B homeroom teacher Ms. Haruka Utsugi by attacking any martial artist he finds and mimicking her fighting style to make it seem that she is the Switcher. Though the Kamen Rider Club learns the truth when Kamen Rider Fourze Magnet States destroying the Pegasus Zodiarts, the Virgo Zodiarts appears when his Zodiarts form resurrects and she facilitates his evolution into the Cancer Zodiarts.
Norio Eguchi is a cosplay otaku at AGHS who watched Fourze during his fight with the Lynx Zodiarts and wanted to be like him yet lacked the nerve. Eguchi receives a Zodiarts Switch from Libra Zodiarts which causes him to develop a split personality with the dark aspects of himself occupying the Cygnus Zodiarts, he takes control of Eguchi's body whenever he is distressed without his knowledge. Eguchi simply remembers what Cycnus has done as a bystander. As the Cygnus, he uses his feathers for multiple purposes from throwing them around to make a grand entrance to using them as shuriken, and has powerful kicks that resemble ballet moves. Portraying himself as a hero, the Cygnus obtains a large following of people called the Ugly Duckling Society, which is led by Misa Toriizaki, who uses a point system to judge people like the Zodiarts does. Cycnus actually wants admiration and will attack anyone who he sees as a threat to his true plan: replacing Fourze, as well as those who refuse to see him as a superior being. When Eguchi is revealed to be the Switcher, having no knowledge that Cycnus was the product of his own mind, the KR Club helps him to perform good deeds before finally revealing to him that he is a Zodiarts. He successfully rejects the Switch and his dark self. The Cancer Zodiarts abducts him so the Ugly Duckling Society can force Eguchi to take the form of their hero. Cycnus uses Misa as a human shield when Fourze arrives, breaking the society's faith in him. After the Cygnus is destroyed by Kamen Rider Meteor, the society disbands while Eguchi lives his dream of being a hero, starting with doing good deeds and now donning a costume resembling Kamen Rider Fourze.
Yayoi Tokuda is a third-year student who is the president of AGHS's school newspaper, having a love for the school. Because of her intense need to discover the truth behind events, she discovers the identities of three former Zodiarts Switchers prior to receiving a Zodiarts Switch from the Cancer Zodiarts. Becoming the Coma Zodiarts, able to use her hair as tendrils or to create clones of others that she controls like puppets, Yayoi's love to stay in school is warped by the Switch, making her think that ruining both the convocation and the prom will allow her to stay in high school forever. Before being revealed, Yayoi creates clones of the Chameleon Zodiarts, the Altar Zodiarts, and the Dragon Zodiarts to run amok in the school while dragging the names of former Switchers through the mud for a scoop to ruin the convocation. However, when that failed, Yayoi resolved to crash the prom after assuming her Zodiarts's Last One state before her Zodiarts body is smashed between Kamen Rider Fourze and the Powerdizer.
Haru Kusao is a meek new first-year student at Amanogawa High School who along with his middle school friend Ran Kuroki is invited by Gentaro to join the Kamen Rider Club. Haru receives a Zodiarts Switch and becomes the Musca Zodiarts, gaining the ability to spit a powerful mucus-like slime from his mouth and to jump long distances. Though Ran tries to talk him into getting rid of the Zodiarts Switch, Haru's refusal to give up such a power causes his Zodiarts form to undergo a metamorphosis into a more powerful second form called Phase 2 where he can break his body up into a swarm of flies, though he cannot quite control this ability. When the Zodiarts Switch's Last One state is reached, the Musca metamorphoses into Phase 3 which is able to fly and shoot light beams. The Musca is eventually defeated when Mr. Ohsugi gives Fourze the Net Switch back, allowing for the Musca to be immobilized. But because of his mental instability, destroying him would only keep him in this state. Only after Ran says that she does not have to protect him is Haru able to become his old self again and is defeated by Magnet States. Later, after returning to his body, Haru is given provisional membership alongside Ran while recuperating from his injuries in the hospital. By the end of the series, Haru and Ran have been made official KR Club members.