Misora Isurugi is a supporting protagonist in Kamen Rider Build. She is a member of the nascita crew and the one who purifies Smash essences to create Fullbottles, the devices Sento Kiryu uses to assume Build's various forms.
On the day of the Skywall Disaster, Misora discovered a golden bracelet that had been recovered from Mars, which clung to her hand and gave her the ability to purify Smash essences, but also caused to fall into a coma for seven years in wake of the Skywall Disaster.
After waking up, Misora was persuaded to join Faust by her father, Soichi Isurugi, who was secretly possessed by Evolt and the astronaut who had excavated the Pandora Box, the artifact which caused the disaster. Misora's role in Faust was to purify Fullbottles for them, believing it was for a good cause. However, Misora eventually learned the truth about Faust and couldn't bring herself to purify Fullbottles for them anymore knowing their true intentions. Since Misora's mental state was necessary for her to purify Fullbottles, Evolt/"Soichi" staged a rescue of Misora and brought her back to the nascita cafe. He then wiped the memories of Faust co-founder Takumi Katsuragi, who had been plotting against him, and swapped his face with that of another man named Taro Satou.
Leaving Takumi in an alleyway, "Soichi" later "discovered" him and brought him back to the cafe, where he renamed him "Sento Kiryu". Setting up a lab in nascita, Sento became Kamen Rider Build and began fighting against the Smash monsters released by Faust and collecting their essences, providing Misora with the impetus she needed to start purifying Fullbottles again, though this unknowingly furthered Evolt's plans.
Kamen Rider X
Kamen Rider Amazon
Kamen Rider Super-1
Kamen Rider ZX
Kamen Rider Black/RX
Kamen Rider Kuuga