Kohei Sato
Kai wrestled his first match as a freelancer at a Pro Wrestling Zero1 event on January 1, 2017, where he defeated Hartley Jackson. The following day, Kai returned to All Japan Pro Wrestling, announcing he would again start wrestling for the promotion in February with the goal of obtaining the Triple Crown Heavyweight Championship. On February 3, Kai received a shot at Zero1's World Heavyweight Championship, but the match against defending champion Kohei Sato ended in a thirty-minute time limit draw. Kai's AJPW return match took place on February 17, when he and Ryoji Sai defeated Joe Doering and Suwama. On March 2, Kai and Yusaku Obata unsuccessfully challenged Akebono and Shogun Okamoto for the NWA Intercontinental Tag Team Championship. In April, Kai took part in AJPW's 2017 Champion Carnival, where he finished with a record of three wins and three losses. On May 21, Kai and Kengo Mashimo won AJPW's World Tag Team Championship by defeating Bodyguard and Zeus. Later that same day, Kai teamed with Yusaku Obata to defeat Hideki Suzuki and Kohei Sato for Zero1's vacant NWA Intercontinental Tag Team Championship, becoming a triple crown tag team champion in one day (the World Tag Team Championship is made up of two titles). Kai and Mashimo lost the World Tag Team Championship back to Bodyguard and Zeus on June 11. On August 27, Kai replaced an injured Jake Lee and teamed with Naoya Nomura in an attempt to regain the World Tag Team Championship, but the two were defeated by Daisuke Sekimoto and Yuji Okabayashi in a match for the vacant title. Three days later, Kai and Obata were stripped of the NWA Intercontinental Tag Team Championship due to Zero1 being unable to book a title defense for the two because of scheduling conflicts. On October 31, Kai took part in Atsushi Onita's retirement match.