Ryusei is a transfer student coming to Amanogawa High from Subaruboshi High School, who put a facade of being a friendly person; when he really kept everything to himself. After his mission is revealed, he drops the facade around the Kamen Rider Club. No Kamen Rider Club members, including Gentaro, knew that he was actually Kamen Rider Meteor, as he was under orders from Tachibana. After the incident with the Aries Zodiarts, the entire Kamen Rider Club, save possibly Ohsugi, know of his identity, and Tachibana tasks them with keeping his identity from the enemy. He first appears after the credits of Movie War Mega Max fighting the remaining members of Foundation X before moving on to Amanogawa High School.
He is a member of the Anti-Zodiarts Union, supported from the satellite named M-BUS and a mysterious being called Tachibana. He started fighting against Zodiarts after witnessing his old friend, Jiro foolishly using a Zodiarts Switch while causing it to self destruct and hospitalize him, putting him in a coma. Unable to forgive himself for failing to prevent Jiro's injury, Ryusei was given a package by Tachibana to become Meteor in order to track down the Aries Zodiarts. Things have started rocky between Meteor and Fourze due to their different objectives. He is however willing to cooperate with Fourze in the battle against the Horoscopes. When he first transferred from Subaruboshi to AGHS, Ryusei sought to join the Kamen Rider Club.
To ensure his mission goes without fail, Ryusei puts up a bright, cheerful, and albeit timid facade so no one would be the wiser. Eventually, during the Kamen Rider Club's battle with the Lynx Zodiarts, Ryusei appears as Kamen Rider Meteor and reveals his agenda to them as he holds Kamen Rider Fourze at bay to ensure the Lynx Zodiarts's escape in hopes that he might evolve into the Aries Zodiarts. After he defeats the Scorpion Zodiarts, Ryusei successfully joins the Kamen Rider Club in order to observe them better and putting up a further facade of being a technical genius, he is entrusted by Gentaro to assist Kengo in the creation of several Astro Switches and the NS Magphone. While going onto the field with the rest of the club members, he plays further on his supposedly timid trait by running away when he sees a Zodiarts, should he need to fight the monster personally.
Though his cover serves him well so far with the rest of the club, he is actually not much of an actor and often lets his principles or his smarts take priority over maintaining his cover. Those with a keen eye like Tomoko and Kijima can detect something off with him based on those "leaks" alone, the latter calling him out to set up a partnership while intending to uncover Kamen Rider Meteor's identity. Kijima eventually manages to trick him into revealing his identity as Kamen Rider Meteor, with Ryusei attempting to silence him before learning that Tachibana was already alerted to his secret being compromised and had shut down the Meteor System as a consequence.
He gets a second chance in redeeming himself and is put in a dilemma between keeping his promise thus saving his Kamen Rider Club friends, and retaining the use of the Meteor System. Ryusei chooses the former, earning Tachibana's approval and gains the Meteor Storm Switch along with retaining the use of the Meteor System. Though he intends to look for the escaped Kijima to settle things with him once and for all to keep his identity covered, he is unaware that Kijima is no longer a threat and told by Tachibana that his cover is now secured.
Unfortunately, when Ryusei meets the Aries Zodiarts when said Horoscopes takes over Subaruboshi High, he begins to lose his focus due to being so close to reving Jiro. So, Aries offers him (or rather, Meteor) a deal; he will revive Jiro in return for killing Fourze. Ryusei accepts. Meteor aids the latter and betrays the Kamen Rider Club, and kills Fourze with a one-inch punch to the chest, near the heart. Disgusted by his actions, Tachibana shuts down the Meteor System, revealing Meteor's identity to the Club and his school friends.
Aries keeps up his part of the bargain and revives Jiro, but despite being awakened from his coma, after Ryusei tells Jirou of what he did, Jiro's health continues to fail. Jiro says he only took the Zodiarts Switch that hospitalized him to be strong like Ryusei, but his weakness dragged Ryusei down. Ryusei feels guilty for betraying the Kamen Rider Club and realizes that he truly did want to be Gentaro's friend.
As a result, he takes on Aries despite having lost his powers and is almost killed until a revived Gentaro intervenes. Ryusei is shocked, and tries to apologize, but Gentarou had already fully forgiven Ryusei for his actions and the two Kamen Riders finally become true friends. After Aries is destroyed, Ryusei is forgiven by the rest of Kamen Rider Club who agree to help keep his identity secret.
While training with Tachibana, he discovers his identity as the Virgo Zodiart and tries to attack him, causing him to be sent to the Dark Nebula. When Gentaro successfully destroys the vase he was ordered to destroy, Tachibana brought back Ryusei and Tomoko from the Dark Nebula, revealing that it was actually the M-BUS. Before Tachibana/Emoto died though, he left the transformation option to automatic, allowing Ryusei to transform without needing authorization and no longer kept his identity as Meteor secret anymore.
Under orders to not reveal his identity as a Kamen Rider and extensive knowledge regarding the Zodiarts menace to anyone, the duplicitous Ryusei hides his scheming, cold and arrogant personality under a bright, cheerful, and albeit slightly timid facade when he is around people. However Gentaro was the only one able to tell that he wasn't honest. He isn't a good actor to begin with and as such on occasions when push comes to shove, bits of his true personality reveal themselves. For example, after the destruction of the Lynx Zodiarts in hopes of reviving Jiro, he hits Gentaro, knocking him down but shattering his doubt of him and convincing him that Ryusei isn't entirely dishonest. Other than his true character, he is also forced to hide his martial arts prowess under a constructed form of cowardice, running away in "fright" in order to find a private place to transform into Meteor.
At first, he never cared about collateral damage to the Kamen Rider Club or pretty much anything, as long as he's able to either stop the Zodiarts himself or save it till it gets to "Last One". However it seems that his feelings for Gentaro and the others began to affect his personality. He succeeded in helping Gentaro and Kengo make up in the fight against the Dragon Zodiarts. He also stopped his punch against Cygnus Zodiarts when it used Tomoko as a shield. Despite his growing affinity for the club, he refuses to think of any of them as friends and goes so far to even acknowledging friendship so in his facade, due to his vow to never make friends again after the incident with his friend.
Ironically, this act later changes again after he meets Aries Zodiarts, as the drive to save his friend had caused him to actually kill Gentaro.
After the incident. Ryusei felt guilty over his crime and the feelings worsen due to his action to save his friend had ironically, worsen his friend's condition. Seeking to atone for his crimes and thinking that he has nothing further to lose, he shows up to rescue the kidnapped club without any regard of his own safety. After Gentaro resurrected, he finally made the decision to become Gentaro's friend and in extension, a friend to the entire Kamen Rider Club. He promises to be a better friend to Gentaro and the rest of the club, and protects Gentaro from Yukina, albeit harshly, deterring the girl with caltrops and physical force. He also shows to be much friendlier to the other members of the club, including Kengo, who inquires about this, and Ryusei insures that he has completely dropped the facade he once carried and appears as his true self.
Kamen Rider X
Kamen Rider Amazon
Kamen Rider Super-1
Kamen Rider ZX
Kamen Rider Black/RX
Kamen Rider Kuuga