Sawa grew up in an orphanage where she was raised as one of the Namba Children. Alongside the other children, Sawa was trained as a spy and conditioned to have complete loyalty to Namba.
Encounters with Build
Sawa interviewed Gentoku Himuro about the Smash, where she asked for his thoughts on the rumored Kamen Rider. Gentoku instead suggested "continuing the conversation" at the nearby hotel, but Sawa predictably rebuked him.
Later that night, Sawa was saved from Needle Smash by Kamen Rider Build. As he canceled his transformation and walked away, he dropped a nascita card, giving Sawa a clue as to his true identity.
The next day, she visits Sento's hideout after Soichi accidentally left the door open. She promises to Sento not to reveal his identity in exchange for him letting her interview him.
True Nature Revealed
However, she was later revealed as a spy for Namba, secretly providing him with photographs of all of Build's Best Match forms thus far. However, Misora finds the audio-recording bug Sawa had planted in their hideout and realizes she is not who she seems.
She soon discovers that her bug is missing, and is confronted by Misora. Sawa attempted to convince Misora that the bug was just a habit for her reporting, but Misora remained unconvinced. Sawa then uses Ryuga's arrival as an opportunity to escape and reports to Namba that her cover has been compromised. She is then captured by Faust and turned into the Stretch Smash. After this was recorded on video, Faust sent it Sento and set her loose in the city, Build tried to fight her off as Build KeyDragon, but the power proved to much for him and he was forced to cancel the transformation. Fortunately for him, Ryuga became Cross-Z and defeated her in one blow before Sento extracted her Smash essence. Sawa then confessed to having been a spy.
Defecting from Namba
Back at nascita, Sawa delves into more detail about her nature as a spy for Namba, and supplies them with a conversation between Namba and Night Rogue she secretly recorded using a voice recorder in her necklace, as well as information on the Pandora Box's current location. She was then chained to a chair in Sento's lab to prevent her from escaping, while Sento and Ryuga went to investigate. She was later unchained by Misora when the two Riders returned.
Sawa later went to visit the hospitalized Taizan Himuro in a bid to convince him that there is connection between Faust and the Touto government. However, Taizan received information that the Touto government is launching an operation to wipe out Faust, causing him to doubt Sawa's report was disproved on the spot and for security to be sent to arrest her, but Sawa escaped.
Kamen Rider X
Kamen Rider Amazon
Kamen Rider Super-1
Kamen Rider ZX
Kamen Rider Black/RX
Kamen Rider Kuuga