Michinoku made his Extreme Championship Wrestling (ECW) debut on February 14, 1997, in a match where he teamed with Dick Togo and Terry Boy to defeat Gran Hamada, Gran Naniwa and The Great Sasuke. This three-on-three feud lasted until ECW Barely Legal 1997, where Gran Hamada, Masato Yakushiji and The Great Sasuke would defeat the trio. This was also Michinoku's first pay-per-view appearance. After this, Michinoku left the company.
He made his World Wrestling Federation (WWF) debut on July 6, 1997, at the WWF pay-per-view Canadian Stampede, losing to The Great Sasuke. He lost a rematch to Sasuke the following night on Raw. He was entered in the WWF Light Heavyweight Title Tournament, where the winner would become the first WWF Light Heavyweight Champion. He beat Devon Storm in the quarterfinal and Aguila in the semifinal. On December 7, 1997, Michinoku defeated Brian Christopher at D-Generation X: In Your House to become the first WWF Light Heavyweight Champion recognized by the WWF. Taka successfully defended the WWF Light Heavyweight Title at No Way Out of Texas: In Your House against Pantera, at WrestleMania XIV against Aguila, and against multiple different opponents on Raw is War and Shotgun Saturday Night. After holding the title for more than ten months, Michinoku lost the title to Christian at Judgment Day: In Your House on October 18.
Taka started to become "Americanised" and on Raw, he teamed with Bradshaw, and segments where shown of Taka and Bradshaw doing generalized and stereotyped American activities. He was soon attacked by Kai En Tai for unknown reasons, which began a feud with Kai En Tai. Michinoku would team up with Bradshaw to take on Dick Togo, Mens Teioh, and Sho Funaki at Over the Edge: In Your House, only to be defeated. He would then also team up with The Headbangers to defeat Togo, Teioh, and Funaki at King of the Ring. With Kai En Tai also feuding with Val Venis, the pair teamed up to take on Togo and Funaki in a tag team match. Taka made a swerve, however, by turning against Venis, proclaiming that Mrs. Yamaguchi-San was his sister. Venis was dragged backstage by Kaientai to be castrated, though the audience did not see what happened next. A few weeks later, Michinoku was involved in a gauntlet match with Togo, Teioh and Funaki to defeat Venis. Michinoku once again teamed up with Togo, Teioh and Funaki to go against The Oddities (Giant Silva, Golga, and Kurrgan) at SummerSlam 1998, only to lose the match. With Kai En Tai in 1998, he had multiple chances to become a champion, going up against Christian and Duane Gill for the WWF Light Heavyweight Championship, and X-Pac for the WWF European Championship.
In 1999, Michinoku would make a short return to ECW at CyberSlam 1999, defeating Papi Chulo. He also wrestled Super Crazy at Hardcore Heaven 1999. Other matches included two tag matches teaming with Yoshihiro Tajiri, a Hardcore Heaven rematch with Super Crazy (ending In another victory for Super Crazy), a loss against Jerry Lynn, and his last two matches for ECW being two wins against Mosco de la Merced.[8]
After Togo, Teioh and both Yamaguchis left the WWF, Michinoku and Funaki began wrestling as a tag team using the name Kaientai. They were primarily comedy jobbers, best known for their "Indeed!" skits in which voices in English were dubbed into their promos while they badly lip-synced. Their first tag team match together came in the form of a loss to the Hardy Boyz. At WrestleMania 2000, the pair were part of a hardcore battle royal for the WWF Hardcore Championship; Funaki even became the Hardcore Champion for a small amount of time, however Michinoku never held the title. Taka's biggest venture in WWF came when he challenged Triple H for the WWF Championship on the April 10, 2000 edition of Raw, coming up short despite interference on his behalf from Funaki and the Acolytes Protection Agency. In 2000, they had a chance to become the number one contenders for the WWF World Tag Team Championship in a number one contendership battle royal in which The APA won. In 2001, Kaientai took on the Dudley Boyz for the WWF Tag Team Championship, but failed to capture them. In 2000 and 2001, Michinoku had multiple opportunities to become the WWF Light Heavyweight Champion, taking on Dean Malenko, Jeff Hardy, and others. In their last match together as Kaientai, due to Michinoku leaving the WWF, they defeated Justin Credible and Raven on the October 20, 2001 edition of WWF Jakked.
In early 2002, Michinoku was released from his WWF contract.