When WWE rebranded NXT into its developmental territory, Ohno debuted on the July 4 episode of the rebooted NXT, where he defeated Mike Dalton, while taking on a gimmick of a methodical wrestler who takes pleasure from inflicting pain and knocking out opponents. Ohno started a feud with Richie Steamboat in September; Steamboat defeated Ohno twice (via disqualification and a cradle), but Ohno conducted successful post-match assaults on Steamboat. Ohno then injured and pinned Steamboat during a six-man tag match while teaming with the Ascension against Steamboat and The Usos on the October 17 NXT, but Steamboat still managed to cost Ohno a match against Trent Barreta a week later. Ohno defeated Barreta in a rematch on the November 7 NXT. After Leo Kruger attacked Baretta before he could face Ohno again on the November 21 NXT, Steamboat returned from injury and decisively pinned Ohno to end the feud. Ohno then formed an alliance with Kruger and also started a feud with William Regal after Regal saved Tyson Kidd from a beatdown by Ohno and Kruger on the December 5 NXT. Ohno and Kruger defeated Kidd and Justin Gabriel on the January 2, 2013 NXT. On the January 30 NXT, Ohno and Kruger entered the NXT Tag Team Championship Tournament to crown the inaugural champions and defeated Alex Riley and Derrick Bateman in the first round. On the February 6 NXT, Ohno and Kruger were defeated by Adrian Neville and Oliver Grey in the semi-finals when Ohno was distracted with taunting Regal. When Regal saved Derrick Bateman from Ohno's post-match attack on the March 13 NXT, Ohno confronted Regal only to be assaulted by him. The following week, Regal apologized to Ohno and in reply, Ohno stated that he had followed in Regal's footsteps to arrive in WWE, but that Regal's whole career had no legacy, leading to Regal again assaulting Ohno. In the following weeks, Ohno and Regal went on to attack each other while the other person was at commentary. The rivalry between Ohno and Regal culminated in a match on the April 11 NXT, which Regal won.
On the May 8 NXT, Ohno turned face by apologizing to Regal, after which, he was attacked by the Wyatt Family. On the May 29 episode of NXT, Ohno competed in an 18-man battle royal to determine the number one contender to the NXT Championship, where he and Corey Graves were eliminated by Bray Wyatt. The following week Ohno and Graves teamed up to take on Luke Harper and Erick Rowan for the NXT Tag Team Championship but were defeated after Wyatt interfered. On the June 19 NXT, Ohno, Graves, and Adrian Neville were defeated by the Wyatt Family in a six-man tag team match. On the June 26 NXT, Graves and Ohno defeated Garrett Dylan and Scott Dawson to become number one contenders for the tag title, but were later attacked by the Wyatt Family as well as Dylan and Dawson. This attack led to Ohno suffering a storyline injury while he was pulled from NXT television tapings, reportedly due to his lack of commitment to physical conditioning programs. Ohno returned to in-ring action on the October 2 NXT, losing to Luke Harper.
On November 8, 2013, Ohno was released from WWE ending his first stint in the company.
In December 2016, it was reported that Ohno had re-signed with WWE. He made his return at the January 5, 2017 NXT tapings, confronting then NXT Champion Shinsuke Nakamura at the end of the live show. The following day, Ohno defeated Andrade "Cien" Almas at an NXT house show in his return match. Ohno returned to NXT television on February 22, 2017, saving No Way Jose and confronting Bobby Roode. On the March 15 episode of NXT, Ohno faced Roode for the NXT Championship in a losing effort. On the March 29 episode of NXT, Ohno defeated Elias Samson in a Loser Leaves NXT match. Ohno made his NXT TakeOver debut at NXT TakeOver: Orlando in an eight-person tag team match, teaming with Tye Dillinger, Roderick Strong, and Ruby Riot against SAnitY, replacing an injured No Way Jose, being on the losing side of the team.
Ohno then entered a program with Hideo Itami. After Itami's loss at NXT TakeOver: Chicago, he began causing a scene in the locker room. Ohno tried to calm down Itami. Concerned with Itami's actions, Ohno saved Oney Lorcan from a post-match attack by Itami on the June 7 edition of NXT. After weeks of trying to help Itami, tensions became too high and Ohno and Itami faced off on the July 26 episode of NXT; Ohno won after Itami got himself disqualified. The two concluded their feud on the September 6 episode of NXT, when Ohno defeated Itami in a No Disqualification match. On the November 8 episode of NXT, Ohno asked general manager William Regal for a match with the undefeated Lars Sullivan. At NXT TakeOver: WarGames, Ohno was defeated by Sullivan. On the January 24 episode of NXT, Ohno had a backstage encounter with Velveteen Dream that ended with Ohno shoving Dream to the ground. This led to a match against Dream at NXT TakeOver: Philadelphia where Ohno lost.
Ohno then began to be very vocal with his displeasure with the attention given to new NXT superstars, and seen as the figuratively gatekeeper in NXT while showing signs of a heel turn. At NXT TakeOver: WarGames, he was called out by Matt Riddle, who challenged him to an impromptu match, in which he lost in only eight seconds. At the December 5 edition of NXT, Ohno attacked Riddle after his match against the debuting Punishment Martinez, cementing his heel turn in the process. At NXT TakeOver: Phoenix, Ohno faced Riddle in a rematch, which he lost. Following him "leaving" NXT, Ohno continued wrestling on NXT live events. On April 10, 2019, Ohno wrestled the recently signed Kushida, in his debut match for NXT.
On February 22, 2019, Ohno debuted at an NXT UK event in Coventry, UK. There it was announced that Ohno was now an active wrestler on the UK brand and had signed a multi-year contract. The following night, February 23, he cut a promo at UK Coventry, reading an apology off his phone for Ashton Smith. Later, he was defeated by Travis Banks. On March 20, 2019, Kassius Ohno defeated Aston Smith.
On April 16, 2020, Ohno was released from his WWE contract.