In March 2017, Shirai took part in a WWE tryout at the WWE Performance Center in Orlando, Florida. After the tryout, Shirai confirmed that she had been offered a contract.
Shirai made her first official appearance for the promotion on June 30, 2018 at the WWE house show in Ryogoku Kokugikan, where it was announced she had signed with the promotion and would be competing in their developmental territory, NXT. In July, it was announced that Shirai would participate in the second Mae Young Classic tournament. On August 8, Shirai defeated Xia Brookside in the tournament's first round in her WWE debut match. The following day, on August 9, Shirai defeated Zeuxis in the second round, Deonna Purrazzo in the quarterfinals and Rhea Ripley in the semi–finals to advance to the finals of the tournament, that took place at WWE Evolution, on October 28, where Shirai was defeated by Toni Storm.
In her first appearance for NXT, Shirai debuted on November 17, 2018, at the NXT TakeOver: WarGames event where she and Dakota Kai saved her best friend Kairi Sane during her match with Shayna Baszler from an assault by her allies Jessamyn Duke and Marina Shafir. On the December 19 episode of NXT, in what was her television debut, Shirai teamed with Kai as the two defeated Duke and Shafir in a tag team match, and because of her win, a week later, Shirai competed in a fatal–four way match to determine the number one contender for the NXT Women's Championship, however, the match was won by Bianca Belair. Shortly after, with Kai sidelined with an injury, Shirai continued to team with Sane, forming a tag team known as "The Sky Pirates" while continuing to defeat various teams.
On April 5, 2019, at NXT TakeOver: New York, Shirai took part in a fatal–four way match for the NXT Women's Championship, however, she was unsuccessful in capturing the title as Baszler submitted Bianca Belair to retain the title. Just six days later on April 11 (episode aired on tape delay on April 17), Shirai interfered in Sane's rematch with Baszler and attacked her as she was looking to injure Sane, resulting in a disqualification loss for Sane. As a result, Sane was not allowed to challenge for the NXT Women's Championship anymore, which was a way to write her off the brand. After Sane left the brand, Shirai continued to feud with Baszler, Duke and Shafir as the three continuously attacked her. This ultimately led to a title match between the two, that took place at NXT TakeOver: XXV on June 1, where Shirai was unsuccessful despite Candice LeRae helping Shirai by attacking Duke and Shafir with a kendo stick. After the match, she attacked Baszler with the kendo stick and a steel chair. This led to a steel cage match between the two, that took place on the June 26 episode of NXT, where Shirai once again failed to capture the title from Baszler, despite LeRae again helping her by taking out Duke and Shafir. Shirai then attacked LeRae herself after the match, turning heel for the first time in WWE. In the following weeks, Shirai developed a new image and began wearing black leather while continued to feud with LeRae. On June 30 edition of NXT, LeRae challenged Shirai to a singles match at NXT TakeOver: Toronto, where she was successful.
In November 2019, Shirai was involved in Baszler's feud with Rhea Ripley when she was chosen by Baszler for her team in the first-ever women's WarGames match alongside Bianca Belair. On the November 13 episode of NXT, Shirai competed in an ladder match against Mia Yim to determine who would get the advantage at WarGames. It was then that the final competitor for Baszler's team was announced when NXT UK Women's Champion Kay Lee Ray interfered with the match by throwing Yim out of the picture and helping Shirai climb up the ladder to secure the briefcase. On November 23, 2019 at NXT TakeOver: WarGames, Baszler's team lost to Ripley and LeRae despite having a 2-on-4 Handicap advantage after Ripley's team member, Dakota Kai (who was a replacement for Yim after she was attacked during the pre-show) turned heel by attacking her best friend and fellow team member, Tegan Nox.
Shirai suffered a minor injury on the January 22, 2020 episode of NXT while competing against Toni Storm. She returned on the March 25 episode by replacing Xia Li in her match to qualify for a ladder match where the winner received an opportunity at the NXT Women's Championship. She defeated Aliyah to earn a spot in the match. On the April 8 episode of NXT, Shirai won the ladder match for an opportunity against the new NXT Women's Champion Charlotte Flair, who had defeated former champion Rhea Ripley at WrestleMania 36. On the May 6 episode, Shirai battled Flair for the NXT Women's Championship in match that ended in disqualification when Flair attacked her with a kendo stick. She was about to tie Shirai's legs up in a submission on the ring post when the returning Ripley attacked Flair, who fled the scene with her championship. Following the incident, Shirai chased after Ripley, interrupting an interview backstage by arguing with her in what would eventually turn out as a brawl to be separated by officials. Shirai battled Ripley in Ripley's first match since WrestleMania on May 20, 2020. At NXT TakeOver: In Your House, she defeated Charlotte Flair and Rhea Ripley to win her first NXT Women's Championship. Shirai showed signs of a face turn during the post match backstage interview when she praised her opponents' toughness out of respect. On the June 17 episode of NXT, Shirai attacked WWE Women's Tag Team Champions Bayley and Sasha Banks, confirming her face turn in the process. She would face Sasha Banks at The Great American Bash, on night one, in a winning effort. On the July 15 episode of NXT, Shirai made her first successful title defense against Tegan Nox before being attacked by Dakota Kai. This led to a match at NXT TakeOver: XXX, where she successfully retained her title against Kai despite interference from Kai's enforcer Raquel González. In September, Shirai renewed her rivalry with Candice LeRae. Their feud sparked two title matches, including the first ever tables, ladders and scares match, in which Shirai was able to retain her title. On the November 18 episode of NXT, Shirai successfully retained her title against Rhea Ripley. At NXT TakeOver: WarGames, Shirai was a part of Team Blackheart (herself, Shotzi Blackheart, Rhea Ripley and Ember Moon) who faced Team Lerae (Candice LeRae, Toni Storm, Dakota Kai and Raquel González) in a losing effort, in which Shirai was pinned by González.
On February 14, 2021, at NXT TakeOver: Vengeance Day, Shirai defeated Mercedes Martinez and Toni Storm in a triple threat match to retain the NXT Women's Championship. On the March 10, episode of NXT, Shirai was challenged by Storm for the title, which she retained. On April 7, in the main event of night one of NXT TakeOver: Stand and Deliver, she lost the title to Raquel González, ending her reign at 304 days.
Shirai made her return on the June 8 episode of NXT. In the following weeks, Shirai allied with Zoey Stark as a tag team. On the June 29 episode of NXT, they won a triple threat match to become the number one contenders for the NXT Women's Tag Team Championship. At The Great American Bash the following week, Shirai and Stark defeated The Way (Candice LeRae and Indi Hartwell) to win the titles. On the September 7 episode of NXT, they defended their championships in a title match against the team of Kacy Catanzaro and Kayden Carter. They successfully retained their titles in a match against Toxic Attraction (Gigi Dolin and Jacy Jayne) on the September 28 episode of NXT 2.0. At Halloween Havoc, in a triple threat Scareway to Hell ladder match against Toxic Attraction and the team of Indi Hartwell and Persia Pirotta, they lost to Toxic Attraction, ending their reign at 111 days.
At WarGames, Shirai teamed with Cora Jade, Kay Lee Ray, and Raquel González to defeat the team of Dakota Kai and Toxic Attraction in a WarGames match. In 2022, Shirai allied with Kay Lee Ray after saving the latter from Toxic Attraction's attack. As a tag team, they then entered Women's Dusty Rhodes Tag Team Classic. They defeated the team of Amari Miller and Lash Legend in the first round, Kacy Catanzaro and Kayden Carter in the semi-finals, and Wendy Choo and Dakota Kai in the finals to win the women's Dusty Cup. Shirai and Ray then decided to challenge Mandy Rose for NXT Women's Championship at Stand and Deliver instead of challenging tag team champions Dolin and Jayne. They failed to win the title in a fatal four-way match at the event.
After a hiatus due to an injury, on July 30, Shirai returned at SummerSlam alongside Bayley and Dakota Kai, with the three being allies and confronting Raw Women's Champion Bianca Belair. Shirai was presented under the new ring name Iyo Sky and joined the Raw brand. On the following episode of Raw, the trio targeted and attacked Becky Lynch, Alexa Bliss, and Asuka. Sky's debut match was against Belair in a non-title match, resulting in no-contest due to interference from Asuka, Bliss, Kai, and Bayley entering the ring and starting a fight. The following week, the trio challenged Asuka, Belair, and Bliss for a six-woman tag team match at Clash at the Castle. Sky and Kai then participated in Women's Tag Team Championship tournament and defeated the team of Dana Brooke and Tamina in the first round, then Asuka and Bliss in the semi-finals, but lost to the team of Raquel Rodriguez and Aliyah in the finals on the August 29 episode of Raw. At Clash at the Castle, the stable of Sky, Bayley, and Kai was officially dubbed Damage Control, and they would go on to win their match against Belair, Bliss, and Asuka. On the September 12 episode of Raw, Sky and Kai defeated Women's Tag Team Champions Aliyah and Raquel Rodriguez in a rematch to win the championship. On the October 31 episode of Raw, they lost their titles to the team of Asuka and Bliss. Sky and Kai then reclaimed the titles at Crown Jewel in a rematch. At Survivor Series WarGames, Damage Control, Rhea Ripley, and Nikki Cross lost to Belair, Asuka, Bliss, Mia Yim, and Becky Lynch in a WarGames match.
In January 2023, Sky participated in the women's Royal Rumble match at the titular event. She eliminated five wrestlers, four of which were done by her, Bayley, and Kai, before being eliminated by Lynch. On the February 27 episode of Raw, Sky and Kai lost titles to Lynch and Lita; ending their second reign at 114 days. The feud resulted in a six-woman tag team match at WrestleMania 39, where the team of Lynch, Lita, and Trish Stratus defeated Damage Control. On the April 10 episode of Raw, Sky won a number one contender's triple threat match by defeating Mia Yim and Piper Niven, and she earned a title match against Raw Women's Champion Bianca Belair at Backlash. As part of the 2023 WWE Draft, Sky, along with stablemates Bayley and Kai, was drafted to the SmackDown brand. At Backlash, Sky was unsuccessful in winning Belair's title. On the June 9 episode of SmackDown, Sky defeated Shotzi to qualify for the women's Money in the Bank ladder match. Sky would go on to win the women's Money in the Bank ladder match at the namesake event. During the match, Bayley interrupted Sky in retrieving the Money in the Bank briefcase; in retaliation, Sky handcuffed Bayley and Becky Lynch together before grabbing the briefcase. At SummerSlam, Sky cashed-in her briefcase on Bianca Belair following a triple threat match against Asuka and Charlotte Flair to win her first WWE Women's Championship. Sky then successfully retained the title against Asuka and Charlotte Flair in a triple threat match at Fastlane in October. On November 4 at Crown Jewel, Sky retained her title against Belair with the help of returning Kairi Sane. At Survivor Series: WarGames, Damage Control lost to Belair, Flair, Lynch and Shotzi in a WarGames match. On SmackDown New Year's Revolution on January 5, 2024, Sky defeated Mia Yim to retain her title. After stablemate Bayley won the 2024 women’s Royal Rumble, Sky and the rest of Damage Control turned on Bayley after she confronted them for talking about her behind her back, kicking her out of the group. Bayley then announced she would challenge Sky for the WWE Women’s Championship at WrestleMania XL. On night two of WrestleMania XL on April 7, Sky lost her title to Bayley, ending her reign at 246 days.
During night two of the 2024 WWE Draft on April 29, Sky was drafted to Raw with the rest of Damage Control. On the May 6 episode of Raw, Sky competed in the Queen of the Ring tournament, where she would defeat Natalya in the first round. The next week, she defeated Shayna Baszler in the quarterfinals, but lost to Lyra Valkyria in the semifinals the following week. On the June 17 episode of Raw, Sky defeated Kiana James and Zelina Vega in a triple threat match to qualify for the Money in the Bank ladder match. At the event on July 6, she was unsuccessful as the briefcase was won by Tiffany Stratton. Sky would go on to turn face for the first time on the main roster with the rest of Damage Control on the July 29 episode of Raw when they began feuding with the newly-formed Pure Fusion Collective (Shayna Baszler, Zoey Stark and Sonya Deville).
Over the next few months, Sky began teaming with Sane as Asuka and Kai recovered from injuries. On the October 14 episode of Raw, Sky and Sane failed to win the WWE Women's Tag Team Championship from Bianca Belair and Jade Cargill after a distraction from NXT's The Meta-Four (Jakara Jackson and Lash Legend). This led to a match between the two teams on the October 22 episode of NXT, but the match ended in a no contest after Chelsea Green and Piper Niven attacked both teams. At Crown Jewel, Sky and Sane failed to win the titles in a fatal four-way match against the three teams, with Belair pinning Niven to retain. On the following episode of Raw, Sky won a battle royal by last eliminating Lyra Valkyria to become the number one contender for the Women's World Championship.