Played by: Fukushi Sota (福士蒼汰).
The main character on Kamen Rider Fourze.
Kisaragi Gentarou is a third year student at Ama High and is Kamen Rider Fourze. His parents died in a traffic accident while he was in third grade. Gentarou ended up living with his grandfather, Kisaragi Goro. Due to his grandfather's job as a motorcycle mechanic for various race circuits, Gentarou was constantly moving and left behind his friend, Joujima Yuuki. It wasn't until the second year of high school when he reunited with Yuuki. While in the cafeteria, Gentarou got on the wrong side of the football team and forced to take some hits because they took Yuuki as hostage. During this beating, the Orion Zodiarts appeared and tried to defend Yuuki from it as a regular human. Utahoshi Kengo was able to force the Orion Zodiarts to retreat.
Gentarou followed Yuuki and Kengo to the Rabbit Hutch where he took the Fourze Driver from Kengo. With a bit of help from Yuuki, he was able to use the belt to transform into Fourze. After defeating the Orion Zodiarts, Kengo allow Gentarou to use the Fourze Driver. With some inspiration from Nozama Tomoko, Gentarou decided to create the Kamen Rider Club so Fourze is now Kamen Rider Fourze. In over the course of time, he added members to the Kamen Rider Club like Kazashiro Miu, JK, Daimonji Shun, and Nozama Tomoko. He initially distrusted Sakuta Ryuusei as he would not show his true side but ended up allowing him to join as an apprentice member after seeing a glimmer of his true side by punching him after defeating the Lynx Zodiarts.
When Gentarou, Yuuki, Kengo, and Ryuusei went to Subaruboshi High to investigate Zodiarts, Gentarou was killed by Ryuusei so Aries could save his friend, Jirou. With the help of Tachibana and Kengo, he was revived with the power of the Cosmic Switch and was able to access his final form as Fourze.
Despite looking like a delinquent with his pompadour haircut and his non-Ama High school uniform, Gentarou is actually pretty nice and willing to socialize with anyone. His main desire is to make everyone his friend which came from his parents being happy every time he made a friend. Gentarou goes to many lengths to make his current and future friends happy such as jumping into canals to find items (love letter and keychain) and going to JK's home town to see his father so he could make JK see reason. He accepts the bad side of people like JK's tendency to use people and forgives them for doing awful things (Ryuusei killing him). He is afraid of the supernatural. Also he doesn't seem to be interested in having a relationship with anyone. Gentarou's greatest strength is the ability to bond with people and thus he actually the best person for the Fourze Driver since the bond between people is vital to survive in space.
As Fourze, he likes to brawl with the enemy but can fight smart with the Switches. He has shown many times that he can use Switches in clever combinations which is necessary for Cosmic States due to its ability to add Switch properties to other Switches.
Uchuu kitaaa!!! or Space kitaaa!!! 宇宙 キター！！
- A slangy way of saying "Space is awesome". Gentarou and Yuuki both tend to say this.
- Kitaa is also used to say "It has arrived" so there are times when they use this phrasing for other things.
Taiman harasete morau ze, or Let's do this man-to-man, Let's settle this one-on-one タイマン貼らせてもらうぜ
- Before Meteor, Fourze would say this as his secondary catchphrase. We use the translation that we do because the phrasing actually has the word "man" in it, but in all honesty, I now think "one-on-one" would be better. This leads to scenarios where Gentarou complains when the enemy summons Dustards or other allies to fight him not one-on-one.
- The phrasing "Let's do this mano-a-mano" is also acceptable, but not preferred since the original meant "let's fight barehanded". Mano means "hands", not "man".
 Kamen Rider Fourze
Suit Actor: Takaiwa Seiji
For Fourze, his different forms are called states. He acquires a new form with every tenth Switch.
 Base States
- Fourze's base form. When he transforms, Gentarou usually says, "Space kitaaa!!! Kamen Rider Fourze! Let's do this man-to-man!" The latter part being "one-on-one" or "mano-a-mano" are acceptable translations, although it should be noted that originally "mano-a-mano" meant "barehanded". He tends to not say this as much after Meteor joins.
- Base States has access to all four switch slots, unlike the other forms that have one or two slots being used to activate the form and in the cases of Elec, Fire and Cosmic can be pulled out of the Fourze Driver only when performing a limit break. (The effect can be mimicked and enhanced by Cosmic States).
- Limit Breaks: Rider Rocket Space Kick!
 Elec States
- From Switch 10, Elec.
- Weapon: Billy The Club - A pun on Biri which is Japanese for "Shock".
- Billy the Rod has three plug slots. The left plug slot is used the Limit Break along with it being the main one for attacks. The center plug slot allows Fourze to shoot out electric slashes at the enemy. The right plug slot allows Fourze to fire multiple electric slashes at once to surround the enemy with.
- Limit Breaks: Rider 10 Billion Volt Break/Shoot/Burst, and Rider Lightning Drill Kick
 Fire States
- From Switch 20, Fire.
- Weapon: Hee-Hackgun - A romanization of Hi haku 火吐く gun, which in Japanese would mean "Fire-breathing gun".
- The gun has a second mode which makes it a fire extinguisher gun. Fourze has the ability to absorb heat based attacks and use that energy to make his finisher stronger.
- Limit Breaks: Rider Explosive Shoot
 Rocket States
- From Super Rocket Switch 1
- In MegaMax, Nadeshiko created the Super Rocket Switch 1 just before Remu Kannagi converted her into a Switch. The Switch allows Fourze to transform into Rocket States. In this form, he becomes orange and allows him to use Rockets on both his arms. It's assumed that Gentarou didn't use this Switch for awhile due to his feelings for Nadeshiko. He recently uses this form to chase Tachibana in his training to achieve Cosmic States by himself.
- Limit Breaks: Rider Tailspin Crusher and Rider Double Rocket Drill Kick
 Magnet States
- From Switches 30 and 31 combined into the NS Magphone. When the Magphone is split apart and inserted, they become like controllers for the NS Magnet Cannon. The NS Magnet Cannon can be used individually with the N and S Magnet Switches. The NS Magnet Cannon can be combined together to repel metal objects and use for the finisher.
- Limit Breaks: Rider Super Electromagnetic Bomber!
 Cosmic States
- From Switch 40, Cosmic. When he transforms into this states, Fourze says, "Using our bond, we will grab on to space!".
- Weapon: Barizun Sword
- In this form, Fourze has access all 40 Astro Switches. This allows him to combine different Switches' powers such as adding the Freeze Switch to the Launcher Switch to allow him to fire freezing missiles. Even the Barizun Sword can benefit from it from this combination power. It also allows Fourze to create warp drives where he finishes off enemies in space.
- Cosmic States only works when the bond of the Kamen Rider Club is strong. If one member decides to quit the club, Cosmic States is unusable.
- Limit Breaks: Rider Great Galaxy Finish
 Movie/Special Forms
 Rocket Drill States
- When Fourze uses the Clear Drill Switch, he becomes Rocket Drill States. It's a combination of Base States and Rocket States with keeping Fourze's Base States head and the rest is Rocket States. It combines the Drill into the Rocket.
- Limit Break: Rider Rocket Drill Blast
 Astro Switches
The Astro Switches allow Fourze to access various abilities to his arms and legs including new states. There are 40 Astro Switches which each one is numbered.
1. Rocket - It attaches a rocket on the right arm. Fourze uses it to take enemies to other locations and used injunction with Drill for Base States Finisher.
2. Launcher - On the right leg, it can fire 4 rockets at the same time but needs Radar to properly guide the rockets.
3. Drill - A drill is attached to the left leg. It's really used injunction with Rocket for Base States Finisher.
4. Radar - On the left arm, it's mostly used as a communicator to the other members of the Kamen Rider Club. It is also used to guide the rockets from Launcher.
5. Magic Hand - Attaches a long, bendy arm to Fourze's right arm. Mostly used to rescue people or in one case, used to swing OOO around.
6. Camera - It creates a movie camera on Fourze's left arm. It's mostly used to power Burgermeal Foodroid but it can be used to analyze the enemy's ability much better than Burgermeal could.
7. Parachute - Deploys three parachutes from Fourze's left arm. Mostly used when he's descending from space.
8. Chainsaw - Attaches a chainsaw to Fourze's right leg.
9. Hopping - Creates a spring on the left leg to allow Fourze to jump around quicker and higher. It was initally hard to use until Gentarou master it.
10. Elec - Sets in the right arm switch slot. Allows Fourze to access Elec States. When initially used, it created the Billy the Rod and made his hand and part of his arm gold. It even create a backlash of electric current that shock Fourze.
11. Scissors - Attaches a pair of scissors on Fourze's left arm. It powers the Potechokin Foodroid.
12. Beat - Creates a speaker on Fourze's right leg. It creates sound waves to disorient the opponent and can be used to hook up electric guitars.
13. Chain Array - Produces a ball and chain from Fourze's right arm.
14. Smoke - From Fourze's right leg, it produces a smoke cloud to disorient the enemy.
15. Spike - Creates a set of spikes on Fourze's left leg. When kicking from the left leg, they extend out to deal more damage on the enemy.
16. Winch - Adds a hook to Fourze's left arm. It's used either bind an enemy or swinging from place to place. It can even transmit the electric current from Billy the Rod to the enemy.
17. Flash - Makes Fourze's right hand into a giant light bulb to blind enemies. Mostly used to power the Hulashake Foodroid.
18. Shield - Produces a triangle shield in shape of a space shuttle on Fourze's left arm.
19. Gatling - Creates a gatling gun on Fourze's left leg.
20. Fire - Sets in the right arm switch slot. Allows Fourze to access Fire States. It is the only States that he had no problem transforming into the first time around.
21. Stealth - Creates a purple triangle on Fourze's right leg that allows Fourze to be invisible.
22. Hammer - Creates a hammer on Fourze's left hand.
23. Water - Produces a faucet on Fourze's left leg. It streams out water.
24. Medical - Produces a first aid kit on Fourze's left arm. It allows Cosmic Energy to be used to heal injuries. It also allows life energy to be used to heal injuries with a special glove when not being used by Fourze.
25. Pen - Makes Fourze's right leg a giant paintbrush. Initially thought it could only be used to write things but its true ability allows the writing to harden and become strong as metal.
26. Wheel - Creates a segway on Fourze's left leg. It allows Fourze to maneuver in tight spaces unlike the Massinger.
27. Screw - Forms a propeller on Fourze's left leg. It is only used to allow Fourze to maneuver underwater.
28. Hand - Produces a hand similar to Magic Hand but on the right leg and not as long. It can do tasks while Fourze is busy with something else.
29. Scoop - Produces a giant scoop on Fourze's right hand. It's mostly used to power the Horuwankov Foodroid. On the Blu-Ray, this is spelled Schop, which is the correct meaning of the word. It's Dutch for "spade" which the Japanese took as a loanword.
30. N Magnet - Goes on the right arm switch slot. When used with S Magnet initially, it created a powerful magnetic field that Fourze wasn't not able to control. Only with the creation of the NS Magphone that its power can be used properly with S Magnet and allows Fourze to access Magnet States.
31. S Magnet - Goes on the left arm switch slot. When used with N Magnet initially, it created a powerful magnetic field that Fourze wasn't not able to control. Only with the creation of the NS Magphone that its power can be used properly with N Magnet and allows Fourze to access Magnet States.
32. Freeze - Creates a mini-freezer on Fourze's right leg. When opened, it produces a mist that freezes water rather quickly. It mainly powers the Softonya Foodroid.
33. Claw - Produces a set of three claws on Fourze's right arm. The first time it was used, Fourze said "Seiya!" the word that Kamen Rider OOO said every time he finished an enemy.
34. Board - Creates a snowboard from Fourze's left leg.
35. Giant Foot - Produces a giant boot on Fourze's right leg. When Fourze stomps the ground with it, a giant boot appears in the air that crushes opponents.
36. Aero - Attaches a vacuum like device to Fourze's left leg. It can suck up the surrounding air and things. Once it's done sucking, it can be immediately used to create a giant whirlwind.
37. Gyro - Creates a giant helicopter propeller on Fourze's left arm. It is used to move Fourze in the air. It also powers the Nuggegyroika Foodroid.
38. Net - Produces a bug catching net on Fourze's right leg. When moving the right leg, it manipulates a giant energy net that captures the enemy.
39. Stamper - Creates a giant piston on Fourze's left leg. When used, it creates a mark on the target that explodes within 15 seconds.
40. Cosmic - Goes on the right arm switch slot. It allows Fourze to access Cosmic States. Initial attempts almost resulted the destruction of the switch.
- Unlike the other members of the Kamen Rider Club, his name is not a reference to a past Rider. Kisaragi is made of the kanji "like" and "moon", so his family name means "like the moon". "Kisaragi" as a single word is the name of the second month of the lunar calendar.
- His given name is yet another something-tarou. The gen in his name means "string from an instrument" but I also notice that in geometry, it means "chord (straight line joining two points on a curve" which is kind of what he does with the various kids in the school.
- The Rou in Gentarou uses the kanji 朗 which has moon as the ending radical, so there's a moon kanji in both Gentarou's family and given name. Most men's names use this Rou/Son 郎 as the end of their given name. Gen's Rou 朗 means "Cheerful, bright".
- When he appeared in the OOO Wonderful Movie, he did not have the pompadour haircut.
- Gentarou appears to enjoy Double Dutching like his actor Fukushi Sota, as shown in Episode 39.