In early 1997, Taka Michinoku, Dick Togo and Terry Boy had a short stint in Extreme Championship Wrestling as BWO Japan (also known as "BWO International") and feuded with the fellow Japanese team of The Great Sasuke, Gran Hamada and Gran Naniwa. The rivalry culminated at ECW's first ever pay-per-view event Barely Legal 1997, where the team of Sasuke, Hamada and Masato Yakushiji (filling in for an injured Gran Naniwa) came out victorious. Following the match, Kaientai would permanently adopt the bWo colors of blue and white as their own.
Kaientaimade their first appearance in the WWF the night after WrestleMania XIV on the March 30, 1998 episode of Raw is War. They attacked Taka Michinoku — who signed with the WWF much earlier — because they felt he had become Americanized since joining the WWE until he later rejoined them. Kaientai was originally referred to by the announcers as Club Kamikaze, but their new manager Yamaguchi-San announced their actual name upon his arrival shortly afterwards.
Their most infamous WWF feud was with Val Venis, who had a porn star gimmick at the time. Yamaguchi was enraged when he was shown a pornographic video of his wife, sleeping with Venis, and threatened to punish both of them. Mrs. Yamaguchi-San was brought to the ring for what was going to be a spanking by Yamaguchi-San using a wooden paddle, but she was rescued by Venis. A week later, just as Venis had finished a match, Yamaguchi and Kaientai showed up with a salami on a table. Yamaguchi proceeded to chop the salami while shouting at Venis, "I choppy choppy your pee pee!". The following week, Venis teamed up with Taka Michinoku 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 have his member amputated, though the audience did not see what happened next. Venis returned after a week, explained that Yamaguchi's sword narrowly missed his genitalia, due to the lights being turned off by John Wayne Bobbitt, broke off his relationship with Mrs. Yamaguchi-San and thus ended the feud.
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 jobbers, best known for their "Evil! Indeed!" skits in which English voices were dubbed into their promos while they badly lip-synced, with Taka ending his "comments" with "Evil!" and Funaki "saying" only "Indeed!". Funaki and Taka's last ever tag team partnership as Kaientai in the WWF was a win over Raven and Justin Credible on the October 20, 2001 edition of WWF Jakked.