| “ | Now, shall we begin the experiment? | „ |
| ~ Build's catchphrase before transforming |
| “ | The rules of victory have been set! | „ |
| ~ Build's catchphrase after finding the winning match |
Sento Kiryu is the title character and main protagonist of Kamen Rider Build. He is a genius theoretical physicist who experiments with Fullbottles to further enhance his abilities as Kamen Rider Build (仮面ライダービルド Kamen Raidā Birudo) to fight against the Faust organization and their Smash monsters.
A man with no memory of his past, he was initially believed to be someone named "Taro Satou" (佐藤 太郎 Satō Tarō), but his true identity turned out to be Takumi Katsuragi (葛城 巧 Katsuragi Takumi), a scientist at the Touto Institute of Advanced Matter Physics and the co-founder of Faust. As the war for Pandora Box breaks out between the three countries, Sento accepts reality for what it is in order end the war that his previous identity had started.
History
Past
Takumi Katsuragi was originally the son of Shinobu Katsuragi, a researcher at the Institute of Space Engineering Technology who supposedly killed himself six months after the Pandora Box triggered the Skywall Disaster that separated Japan.
Katsuragi eventually rose to be genius scientist himself and a researcher at Touto Institute of Advanced Matter Physics, heading the research of the Pandora Box. who was "murdered" by upon discovering his true identity. Seeking a way to carry out illegal human experimentation, Katsuragi co-founded Faust with Night Rogue and Blood Stalk. He would go on to create the Build Driver, the Fullbottles, the Sclash Driver, the Sclashjellies and the Transteam system.
However, Katsuragi later discovered both Night Rogue and Blood Stalk's true identities, as well as Stalk/Evolt's plans for the Pandora Box and connection to Ryuga Banjou. Katsuragi plotted to stop Evolt, luring Banjou to his house so he could kill him. However, before he could do so he was knocked out by Stalk. Stalk then swapped Katsuragi's identity with a man named Taro Satou, wiped his memories and killed Satou so he could frame Ryuga Banjou for it.
After being experimented on by Faust, Katsuragi was placed in an alleyway by Stalk, who then reverted to his civilian identity of Soichi Isurugi and "found" Katsuragi, giving him the new name of "Sento Kiryu".
As Sento Kiryu
Setting up shop in the basement of Isurugi's cafe "nascita", Sento continued to conduct experiments with the Fullbottles and used the Build Driver to become Kamen Rider Build to defend Touto from the Smash monsters. He soon came across Ryuga Banjou, now an escaped fugitive after having been framed for Katsuragi's murder. Believing Ryuga when he said he didn't do it, Build helped him escape from the Touto Guardians pursuing him.
Sento Kiryu initially believed himself to be Taro Satou after he was recognized by a friend of Satou's, Tatsuya Kishida. However, he later learns from Gentoku Himuro that he was in fact Takumi Katsuragi, having had his face swapped with Taro Satou's by Blood Stalk. Sento also discovers that Blood Stalk is actually his friend and former mentor Soichi Isurugi, and was just using him to get his daughter Misora Isurugi to purify Fullbottles again.
When Touto is invaded by Hokuto with support from Stalk and Faust, Sento and Ryuga find themselves forced to ally with their old enemy Night Rogue aka Gentoku Himuro, who had become acting Prime Minister of Touto following his father falling ill. Thus Sento and Ryuga become "weapons of war" used to combat Hokuto's Kamen Rider Grease and the Hard Smash trio, Hokuto Three Crows. Sento later fought Grease in a representative match to decide who would gain possession of Pandora's Box and managed to defeat him with the power of Hazard Trigger. However, right after this Hokuto was invaded and conquered by Seito due to having no troops behind to safeguard their territory. Seito then declared war on Touto, and Sento was forced to go to war once again. Joining him in his fight against Seito was Kazumi Sawatari / Grease, who sought to free his homeland from Seito. Sento would eventually encounter an old enemy in this war, Gentoku Himuro, who had gone to Seito after being banished once his ties to Faust came out and become Seito's Kamen Rider, Kamen Rider Rogue.
Touto was later challenged to a representative match to decide the fate of Pandora's Box and Japan, and so Build, Cross-Z and Grease fought Seito's Rogue, Remocon Bro's and Engine Bro's in a 3-on-3 Representative Battle. After Grease won his match against Engine Bro's and Cross-Z lost his against Remocon Bro's after he became Hell Bro's, it was up to Sento to win the match for Touto. Transforming into Build, Sento unveiled his new form Build RabbitRabbit and with it initially had the advantage over Rogue. However, Seito had gained the data on Build RabbitRabbit from Sawa Takigawa, who was actually a spy they had planted in Team Build and blackmailed by holding the Nabeshima family hostage. Seito downloaded the data into Rogue, giving him the upper hand against Build. However, unbeknownst to them, Sawa had grown to care for Sento and co. after being treated like family by them and secretly worked with Sento to outsmart them by only leaking half the information. Once the Nabeshima family had been rescued by Grease, Sento unveiled the other transformation he had worked on, Build TankTank, and with that form defeated Rogue.
Despite Seito losing the representative match, Seito's backers Namba Heavy Industries attempted to pressure Seito Prime Minister Masakuni Mido into continuing the war against Touto. When Mido refused and prepared to abide by his word and turn over the Pandora Box, he was killed by Blood Stalk, who transferred his face and appearance onto President Namba so he could act as the Prime Minister. Sento and Team Build later learned this from Gentoku, who sought to defect but was unable to due to Namba implanting a remote explosive chip in him. Sento also eventually discovered that Blood Stalk's true identity was an alien being named Evolt who was possessing Soichi Isurugi's body and had in the ancient past annihilated the civilization of Mars with the power of the Pandora Box. He also discovered that two of his friends also had extra-terrestrial ties: Ryuga had been fused with Evolt's DNA while still in the womb and Misora's bracelet contained the spirit of Mars' Queen Vernage, which gave her the power to purify Fullbottles.
Before Sento could ponder any longer on these developments Touto Prime Minister Taizan Himuro was kidnapped by Seito's forces. During the operation to rescue him, Sento freed Gentoku by altering the signal of the explosive chip, no longer forcing him to serve under Namba. However, Stalk also regained his Evol Driver, enabling him transform into Kamen Rider Evol as he had millions of years ago, and killed Taizan.
Evolt later shifted hosts from Soichi to Ryuga, possessing him to gain back his DNA. Sento attempted to sacrifice himself by overclocking his Hazard Level to destroy both him and Evolt, but this only enabled Evolto to possess him instead. Evolt eventually abandoned Sento as a host after gaining enough power to use the Evol Trigger, making it so he no longer needed a host. However, because of Evolt's possession, Sento regained his memories as Takumi Katsuragi and reverted back to his old self.
Katsuragi developed the Genius Bottle to combat Evolto, but was unable to use it due to lacking the same drive for love and peace that had motivated Sento. Katsuragi thus allowed his Sento personality to return while he split off and became a split personality in Sento's head.
Evolt meanwhile destroyed Namba Heavy Industries and usurped control of Seito by assuming the identity of Masakuni Mido. He was also revealed to be working with Sento's thought-to-be-deceased father, Shinobu Katsuragi, to obtain the 10 Lost Bottles and insert them into the Black Pandora Panel. In pursuit of this goal Evolt finished conquering Japan, destroying the Touto government building, and unified it under a new government created by him, as well as slandering the Kamen Riders as terrorist rebels and framing them for causing destruction with help from Mad Rogue.
Unbeknownst to Team Build, Shinobu was secretly working to destroy Evolt and after setting up Evol to be destroyed in battle against the Touto Riders revealed his true intentions to Team Build. However, Evolt knew of Shinobu's treachery and secretly split off a fraction of his DNA to go possess Utsumi before the battle. After his main body was destroyed, Evolto returned in Utsumi's body and reclaimed his Evol Driver, using it to transform into Kamen Rider Evol Black Hole and kill off Shinobu. With all the Lost Bottles obtained now, Evolt inserted them into the Black Pandora Panel and shoved it into himself, enabling him to assume his true Feverflow form. However, the four Touto Kamen Riders were able to force the panel out of him by Rider Kicking him at the same time. Sento then knocked two of the Fullbottles from the Pandora Panel, preventing Evolto from assuming his true form.
After the "Build Annihilation Plan" incident, Sento discovered data for a White Pandora Panel in his father's research. The White Pandora Panel could be used to destroy Evolto by using him to power the merging of the World of Build into an alternate world, creating a "New World" and in the process reviving everyone who had died. Sento and the other Kamen Riders were later challenged to a final battle at the Pandora Tower by Evolto after he revealed himself as an alien impersonating Masakuni Mido on national television. The four Riders met Evolto at the base of the tower where he explained the rules of their confrontation: they would have to reach the top of the Pandora Tower and for every 10 minutes they didn't he would destroy a section of Japan.
While Sento, Ryuga and Gentoku managed to reach the top of the tower and were soon joined by Misora and Sawa, Kazumi died after using the Blizzard Knuckle Sento had developed to transform into Kamen Rider Grease Blizzard and defeats Lost Smash clones of the Hokuto Three Crows to obtain their Lost Bottles for the White Pandora Panel. At the top of the Tower, Evolt snatched back the Lost Bottles Sento had and used them to assume his Feverflow form once again. Sento, Ryuga and Gentoku transformed into their Kamen Rider forms but were devastated by the tremendous power of Evolto. However, after hearing the cheers of the people of Japan, Gentoku refused to give up and kept on fighting, damaging the Evol Trigger but also being killed by Evolto. Gentoku's damage to the Evol Trigger though caused Evolto to be stunned for a bit, enabling Build and Cross-Z to force the Black Pandora Panel out of him and combine it with the White Pandora Panel to begin the process of merging the World of Build with the main Kamen Rider world. However, in the process, Cross-Z sacrificed himself to drag Evolt in the crack between the two worlds, causing Build to chase after him to rescue him.
Sento travels into the rift between the two worlds and finds Ryuga lying on the ground, though it turns out to really be Evolt in disguise. Evolt reveals to Sento that since he has survived, the merger will cause the two worlds to collide and destroy each other unless he can be defeated. Sento transforms into Build RabbitRabbit to fight him, but is quickly overwhelmed and knocked out of his transformation. Evolt then mocks Sento and tells him he is nothing more than a "sham hero" he created. However, Sento rejects this and states that Build was created and built up by his friends. Evolt then prepares to finish Sento off, but is stopped by Ryuga resisting him from the inside. Ryuga gives Sento some words of encouragement, telling him that his friends all believe in him and spits out the Dragon Fullbottle before Evolt fully consumes him. Sento then transforms into Build RabbitRabbit and fights Evolt again. As the two battle, both begin to fade, causing Evolt to question which one of them will die first. Sento later switches to Build TankTank after being overpowered as Build RabbitRabbit, and later again to Build Sparkling form which he uses to destroy Evolt's Evolti Graspers and Evolti Blasters before eventually being knocked out of that form and back to his base form as Build RabbitTank. With both down to their base Build uses the Rabbit and Dragon Fullbottles to transform into Build RabbitDragon and uses his finishing move on Evolt. Evolt attempts to stand his ground, but is ultimately overpowered by Build and destroyed. Evolt's energy is then used to complete the fusion of the two worlds, thus creating a world where Evolt never existed and where the Skywall Disaster never happened.
In the new world, Sento wakes up clutching a Ridewatch. He goes to the nascita cafe but finds that neither Misora nor Soichi remembers him, with Soichi mistaking him for Taro Satou of Lynks. As Sento walks outside and sits down, he is approached by Ryuga, who complains to him that the new world Ryuga is dating his girlfriend Kasumi. Happy to see one person who remembers in the new world, Sento and Ryuga ride off on the Machine Builder to find a place for themselves in the new world.
New World
However, their peace was soon threatened once again by Killbus, the King of the Blood Tribe and older brother of Evolt. Emerging through the White Pandora Panel, Killbus ambushed Sento and stole his Build Driver, allowing him to transform into Kamen Rider Killbus. After Killbus uninentionally restored the memories of all who had been experimented on by Nebula Gas, Sento met with his old friends to discuss with them the threat of Killbus. To defeat the Blood Tribe King, Sento and co. were ironically forced into an alliance with their old enemy Evolt, who had regenerated himself through cells he had placed in Ryuga.
Sento developed the Muscle Galaxy Fullbottle for Ryuga to transform with, which Ryuga and Evolt used to to transform and merge into Kamen Rider Cross-Z Evol. With their new powers, Cross-Z Evol defeated Killbus with three of their finishers, destroying the Blood Tribe King and restoring peace once more.
Gallery
 Heroes
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