[2] Though pushed for most of his career as an undercarder without any major championship wins, Ishii gathered a cult following,[5][6][7] and in February 2013 was called "probably [one of the] most underrated guys in the business" by Dave Meltzer of the Wrestling Observer Newsletter.

[25] In October 2009, Ishii received some exposure in North America, when he was featured in Total Nonstop Action Wrestling's (TNA) Global Impact 2 program on Spike TV, working in an eight-man tag team main event, where he, Giant Bernard, Karl Anderson and Takashi Iizuka were defeated by Kevin Nash, Kurt Angle, Masahiro Chono and Riki Choshu.

[28][29] On January 4, 2010, Ishii was involved in another big eight-man tag team match at Wrestle Kingdom IV, where he, Takashi Iizuka, Toru Yano and Abdullah the Butcher were defeated by Manabu Nakanishi, Masahiro Chono, Riki Choshu and Terry Funk.

[39] In June 2011, Ishii took part in the J Sports Crown Openweight 6 Man Tag Tournament, where he and Chaos stablemates Takashi Iizuka and Toru Yano made it to the semifinals, before losing to Giant Bernard, Jyushin Thunder Liger and Karl Anderson.

[40] After having worked for NJPW for eight years, Ishii received his first title shot in the promotion on May 20, 2012, when he unsuccessfully challenged Hirooki Goto for the IWGP Intercontinental Championship in the main event of a show in Osaka.

[42][43] The following month, Ishii teamed with Chaos leader Shinsuke Nakamura in the 2012 World Tag League, where they picked up three wins out of their six matches, failing to advance from their round-robin block.

[63][64][65] "Ishii is the ultimate example of a guy who was destined to just be a decent worker on the undercard, who garnered a cult following in Tokyo, which spread to the rest of the country and resulted in him getting a push."

[67] Ishii main evented the second night of the tournament in Korakuen Hall, where he picked up a major win over six-time IWGP Heavyweight Champion Hiroshi Tanahashi.

[68][69][70] On the fourth night of the tournament, Ishii defeated Katsuyori Shibata in a match that received widespread acclaim, including a five-star rating from Dave Meltzer.

[73][74] Following the tournament, NJPW announced that Ishii would embark on his first tour with Mexican promotion Consejo Mundial de Lucha Libre (CMLL) starting September 8.

[94] On May 3 at Wrestling Dontaku 2014, Ishii made his third successful title defense against Tomoaki Honma and was afterwards challenged by IWGP Junior Heavyweight Champion Kota Ibushi,[95][96] with whom he had had sporadic heated encounters since the past year's G1 Climax.

[102][103][104] From July 21 to August 8, Ishii took part in the 2014 G1 Climax, where he finished tied fifth in his block with a record of five wins and five losses,[105][106] working his two final matches with a separated shoulder.

[107] Ishii's performance in the tournament was praised, with Mike Sempervive of Wrestling Observer Newsletter stating that the quality of his matches, his fortitude, popularity and charisma secured him as a "legitimate New Japan star".

[116][117][118] On February 14 at The New Beginning in Sendai, Ishii defeated Tomoaki Honma, a late replacement for an ill Togi Makabe, to win the now vacant NEVER Openweight Championship for the third time.

[140] At the following day's Ring of Honor Wrestling tapings, Ishii successfully defended the title against Cedric Alexander to return to Japan as the reigning champion.

[161][162] Over the weekend of July 1 and 2 at G1 Special in USA, Ishii took part in an eight-man tournament to crown the inaugural IWGP United States Heavyweight Champion, making it to the finals, before losing to Kenny Omega.

[180] At the G1 Supercard the following month, Ishii entered the pre-show Honor Rumble, a 30-man battle royale for a ROH World Championship title match, which was ultimately won by Kenny King.

[187] In the 2019 World Tag League, Ishii and Yoshi-Hashi finished with twenty-two points in the block, behind Guerrillas of Destiny (who they defeated on the final day), Los Ingobernables de Japón (Evil and Sanada) and FinJuice (David Finlay and Juice Robinson).

[188] On January 5, 2020, during the second night of Wrestle Kingdom 14, Ishii unsuccessfully competed in a four-team gauntlet match for the NEVER Openweight 6-Man Tag Team Championship with Yoshi-Hashi and Robbie Eagles.

[195] On the Road to the New Beginning tour, Chaos and Bullet Club would be involved in six-man tag team matches, and on February 1, White returned to the company, attacking Ishii.

[196] The next day, Bullet Club defeated Chaos in a ten-man elimination match, resulting in White and the Guerrillas of Destiny challenging Ishii, Goto and Yoshi-Hashi for the NEVER Openweight 6-Man Tag Team Championship.

[202] Afterwards, Ishii returned to the six-man title picture during the spring and summer tours, where Chaos retained over trios representing Bullet Club,[203][204] Los Ingobernables de Japón[205][206] and Suzuki-gun,[207] as well as the veteran pairing of Tencozy and Yuji Nagata.

[209] On October 21, at the G1 Climax finals, Ishii, Goto and Yoshi-Hashi were defeated in a trios match by Bullet Club sub-group House of Torture (which also included former Chaos member Sho).

[214] On February 13, during the New Years Golden Series tour, he was defeated by Evil in the rematch for the NEVER Openweight Championship, with members of Chaos and House of Torture acting as lumberjacks.

[216] Ishii was announced as a part of the NJPW bracket to qualify for a chance to advance to Forbidden Door to compete in a four-way match for the inaugural AEW All-Atlantic Championship.

[217] However, it was later reported that Ishii had suffered a left knee injury and was not medically cleared to compete at Forbidden Door, therefore Connors took his place in the four-way match, but failed to win.

[227] The following month at Dominion 6.4 in Osaka-jo Hall, the trio defeated AEW's Blackpool Combat Club (Jon Moxley and Claudio Castagnoli) and Shota Umino, therefore retaining their titles.

From November 25 until December 6, Ishii and Toru Yano took part in the 2023 World Tag League, finishing the tournament with a record of four wins, and three losses, failing to advance to the semifinals of the tournament On January 24, 2024, after successfully defending the NEVER Openweight 6-Man Tag Team Championship against TMDK (Kosei Fujita, Mikey Nicholls, Shane Haste), Okada decided to vacate the titles, due to him leaving NJPW, ending their reign at 266 days.

[233] Ishii made another appearance on the Thanksgiving Eve special episode of Dynamite on November 23, facing Chris Jericho, for the ROH World Championship, however, he was defeated.

[234] On the June 28 episode of Dynamite Ishii returned to AEW, facing Jon Moxley in a rematch from their critically acclaimed encounter in the G1 Climax 4 years prior.