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 but getting a huge reaction from the crowd. 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 quarter final, Aguila in the semi final. 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 WWF In Your House 20: No Way Out Of Texas against Pantera, WrestleMania XIV against Aguila and against multiple different opponents on Raw is War and Shotgun Saturday. After holding the title for more than 10 months, Michinoku lost the title to Christian on October 18, 1998.
Taka was attacked by Kai En Tai for unknown reasons. Taka began feuding with Kai En Tai. Michinoku would team up with Bradsaw to take on Dick Togo, Mens Teioh & 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 & 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 & 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 Gillberg for the WWF Light Heavyweight Championship and X-Pac for the WWF European Championship.
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 lose 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 condentors 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.