Sawa Takigawa

Sawa Takigawa (滝川 紗羽) is a journalist investigating the Pandora Box. She aids Sento Kiryu by providing him with information. Later, she was revealed to be working for Jusaburo Nanba as a spy to watch over Build, though this was, in reality, so that she could find a connection between Nanba and the Touto government. She later became one of the victims of Faust's experiments and was turned into the Stretch Smash (ストレッチスマッシュ) after her cover was compromised. Her Smash essence was used as the basis for the Octopus Fullbottle.

Past
Sawa's father was a researcher working for Nanba Heavy Industries. Three years ago, when Faust lost one of the panels of the Pandora Box, a gas explosion occurred at one of Nanba's laboratories, with her father among the eleven researchers who had died in that explosion. The explosion was supposedly set up by the Touto government to cover up the loss of the panel. In order to find out the truth behind her father's death, Sawa began working for Nanba under the pretext of helping spy and gather information on Build. In reality, this was because she wanted to prove a connection between Nanba and the Touto government.

Present
Sawa came to Gentoku Himuro for information about the Smash, as well as his thoughts on the rumored Kamen Rider. Much to her disgust, Gentoku suggested "continuing the conversation" at the nearby hotel. Later that night, Sawa herself was saved from Needle Smash by Kamen Rider Build. When he canceled his transformation and walked away, he dropped a nascita card and Sawa was able to put two-and-two together.

The next day, she visits the hideout after Soichi accidentally left their hideout door open and promises not to reveal Sento's identity on the condition that he gives her an interview. Later she gets them a photo of Nabeshima, the lead suspect in Ryuga's framing case.

After photographing Build's battle with the Flying Smash (and annoying him with her excited commentary), she joins Ryuga in traveling to Seito via smuggling ship to rescue Nabeshima's wife and daughter from Faust. They escape Faust Guardians and bringing them back only to discover that Faust experiments have erased Nabeshima's memories, but the family vows to make new ones.

She later tracks down Tatsuya Kishida, Sento's roommate and bandmate from before his amnesia.

She tells Sento about the Sky Road to Hokuto so he can track down Takumi Katsuragi's mother.

Her true allegiances are revealed when she secretly provides Jusaburo Nanba with photographs of all of Build's Best Match forms thus far, seemingly not for the first time. They discuss the plan for Faust to steal the Pandora Box, which will put Seito and Hokuto on high suspicion, forcing the Touto leader to prepare for war by adopting the Kamen Rider System. However, Misora finds the audio-recording bug Sawa had planted in the hideout.

She soon discovers that her bug is missing, and is noticed by Misora as she attempts to look for it. As Sawa attempts to leave, Misora confronts her, and she unsuccessfully tries to pass the bug off as just a habit for her reporting; however, she manages to slip away when Ryuga arrives, Misora being unwilling to reveal Sawa's suspicious activity just yet. Sawa reports her compromised cover to Nanba, but is quickly intercepted by Faust and turned into the Stretch Smash, which was recorded on video and sent to Sento. Let loose in the city, Build KeyDragon tries fighting her, but the Dragon Fullbottle's power is too much for his body and cancels the transformation. After Ryuga manages to become Cross-Z, he defeats the Stretch Smash in one blow, but she is left on the sidelines until after Night Rogue is fought off, with Sento extracting her Smash essence. Realizing what had happened, she admits to having been a spy.

Back at nascita, Sawa reveals her true motives as a spy to Sento and gang, along with a conversation between Nanba and Night Rogue she secretly recorded using a voice recorder within her necklace. After she provided information on the Pandora Box's current location, she was later chained to a chair at Sento's lab to prevent her from escaping. As Sento and Ryuga went to investigate, she told Misora about the incident regarding her father. She was later unchained by Misora when the two Riders returned.

Sawa, having taken a picture of one of the Box's panels, went to visit the hospitalized Taizan Himuro in a bid to convince him that there is connection between Faust and the Touto government. However, after Taizan received information that the government is launching an operation to wipe out Faust, Sawa's report was disproved on the spot. Two security officials were immediately deployed to arrest her, though she was able to escape.

Sawa and Sento later witnessed Touto's operation to take down Faust, where Nariaki Utsumi was seemingly exposed as "Night Rogue" and Faust's creator, before being gunned down by Gentoku Himuro. Regrouping at nascita, they found out that all the evidence gathered from Faust's hideout pinned everything onto Utsumi, with no implication of any involvement by Touto or Nanba. Having believed that her job was done and that she was no longer needed, Sawa decided to leave, though she was persuaded to stay and continue helping Sento and the others, which she gladly agreed.

Alongside Misora, Sawa was a spectator at the proxy battle between Build, representing Touto, and Grease of Hokuto. Learning that Misora was holding Sento's killswitch which would break the Hazard Trigger at the cost of his life, Sawa rushed back to Nascita where she urged Banjo to intervene, leading him to save the lives of both Kazumi and Sento.

Personality
Sawa is an enthusiastic and energetic woman, whose often bubbly demeanor masks her passionate and shrewd nature.

She also quite Greedy and Money-oriented in her actions, as she demands Sento (and eventually Kazumi) a large sum of money for calling Ryuga to stop Rampaging Sento and for Misora Handshake respectively

Portrayal
Sawa is portrayed by Yukari Taki (滝 裕可里) who previously portrayed portrayed Aoi Katsuragi in Kamen Rider W Returns: Kamen Rider Accel and Mari Shirase in Kamen Rider Ghost.