Gentaro lives with his grandfather Goro kisaragi after his parents died in a traffic accident when Gentaro was in third grade. His parents had a job that (as Gentaro stated) went above both his and his grandfather's head, but they always were proud when their son made friends. His father also told him that he needed to keep his friends close because they would eventually help him out in the long run.
Gentaro is shown to become increasingly adept in using the Kamen Rider Fourze system as the series progresses. He is shown to only be able to use conventional fighting moves, and has to rely on Kengo's advice on which Astro switches to use in battle situations early in the series. As he gets increasingly used to fighting the Zodiarts, he learns how to devise strategies on the fly (though they do not always work and Kengo still needs to be around most of the time) and is seen to be using and changing Astro switches more often. He is shown to be very resourceful with the use of Switches as he learns how to utilize each one in unusual ways, such as using Limit Breaks of Launcher, Gatling and Fire Switches together to form a long range Limit Break finisher, and Limit Breaking the Rocket and Drill Switches twice when he cannot finish Scorpio off with just his usual Rocket Drill Space Kick. When he has difficulty with properly using a Switch, he will take the time to understand it as he did with the Hopping Switch, ending up capable of using it as a weapon instead of just a tool.
Gentaro is a friendly indivual, willing to see the good before the bad and tries his utmost to make people happy as he desires to be friends with all the people he can, but he can be dense at times but also intelligent during battle, making attacks literally, on the fly when he is adept enough in the Fourze System.
A delinquent Yankee-like appearance wearing a short jacket over a T-shirt and baggy pants, with his hair in a pompadour, rather than the clean cut uniform worn by other students, he says this is because he believes there should be freedom what chocie of clothes a man wears.
- Gentaro is the youngest main protagonist Kamen Rider to date, being only a second year high school student when he debuted and a third year after his final victory.
- In Kamen Rider x Kamen Rider Fourse & OOO: Movie War Mega Max, Phillip mentions that Gentaro looks similar to his partner, Shotaro Hidari, this most likely references to his carefree personailty and wanting to make sure his friends don't cry, while Shotaro wants to protect Futo and stop it's inhabitants from crying, , they aren't the same actor however.
- Fourze is currently to date, the only Rider who is able to combine two different Rider powers when using Meteor Fusion States, acquiring Meteor's Jeet Kun Do style, enchaning the Astro Switches he also uses along with Meteor Galaxy used by Kamen Rider Meteor in Storm State, making him more dangerous to his foes, as well to compensate for the loss of use for the Arm Switch Basements, a flaw that is also seen in Magnet States, however in Movie War Ultimatium, Fourze utilizes the Fusion Switch to borrow Kamen Rider Meteor and Kamen Rider Nadeshiko's powers, effictively becoming Kamen Rider Fourze Meteor Nadeshiko States, using two different Rider powers as a base, Nadeshiko using a copied form of the Fourze Driver but with only two slots available instead of the usual four.
- Fourze's Series was actually the 40th anniversary of Kamen Rider, developing 40 Astro Switches for him to utlize in the Series, if you don't count the Extra Switches he obtains in the Movies.
- Currently to date, Gentaro is the only Rider who willingly destroyed his own Driver and in turn, not able to become a Kamen Rider to help a student of his find his own power which gives birth to Inazumaman, Kengo does say however, the Fourze Driver will return to Gentaro cause he befriended the Driver itself, so Kengo says, whenever this is true or not, is up for debate as most previous Riders haven't destroyed their belts willingly, the other Rider to have his Driver destroyed is Kamen Rider Decade Violent Emotion when he allowed Kamen Rider Kivala to run him through the waist, killing Tsukasa Kadoya had if it not been for Natsumi taking a Photo of Tsukasa beforehand and all the Riders Tsukasa met remember his existence and brought him back to life.
- Due to a recent trade between WhiteRose-Aki and StardustXtreme, Gentaro is now controlled by WhiteRose-Aki while StardustXtreme has control of DMC Vergil.