While Kobayashi did not win a lot of matches he made a name for himself with his ability to execute the knife edge chop on opponents with such force that it makes a very loud sound on impact, partially by actually hitting opponents with full force instead of the normal, more "theatrical" version used in professional wrestling.

[10][11] He was also part of IWRG's 2012 Festival de las Máscaras, he, Imposible and Comando Negro defeated the team of Centvrion, Matrix, Jr. and Panterita.

[15] A few weeks later he won the vacant DTU Alto Rendimiento ("High Performance") Championship as he outlasted Dinastía, Eterno, Flamita, Principe Halcón, Rocky Lobo and Tribal.

On March 16, 2013, Eita, Fénix, Freelance and Mike Segura defeated the tema of Cerebro Negro, Dr. Cerebro, Kaving and Kortiz on a show that was supposed to be the retirement of Kaving and Kortiz's father Ray Mendoza, Jr.[31] On July 19, Eita made an appearance for AAA, representing the Los Perros del Mal stable in a six-man tag team match, where he, Daga and Psicosis were defeated by Dark Cuervo, Dark Espíritu and Dark Ozz.

[32] On July 21, 2013, Eita, T-Hawk and U-T, forming a new stable named Millennials, announced their impending return to Dragon Gate.

[37] On December 5, Eita, T-Hawk and one of Millennials' newest members, Mexican wrestler Flamita, defeated Mad Blankey (BxB Hulk, Cyber Kong and Yamato) to win the Open the Triangle Gate Championship.

[39] On December 22, Millennials lost the Open the Triangle Gate Championship to the Jimmyz (Jimmy Susumu, Mr. Kyu Kyu Naoki Tanizaki Toyonaka Dolphin and Ryo "Jimmy" Saito) in a three-way elimination match, which also included Oretachi Veteran-gun (Cima, Dragon Kid and Masaaki Mochizuki).

On July 20, Eita and T-Hawk defeated Akira Tozawa and Shingo Takagi to win the Open the Twin Gate Championship.

[43][44] Afterwards, Eita remained together with former Millennials stablemate Kotoka, with the two starting a feud with T-Hawk, whom they blamed for the dissolution of the stable.

[46] On October 8, he formed a new unit with Cima, Gamma, Punch Tominaga, El Lindaman, and rookies Takehiro Yamamura and Kaito Ishida, which was named Over Generation on November 1.

On November 8 Eita rejoined VerserK after turning on Dragon Kid revealing to be their newest member, which led them to win Early Christmas Tag Team Tournament by defeating BxB Hulk and Kzy in the finals.

On March 7, Tribe Vanguard won the four-way eight-man tag team elimination match, after Ben-K accidentally attacked Kanda.

On April 28, Eita cost Ben-K and Shimizu against KAI and YAMATO, leading them to lose the Open the Twin Gate Championship.

Later that month, Eita took part in the 2019 King of Gate, where he won his block with a clean record of five wins, advancing to the semifinals of the tournament.

The following day, Eita and Shimizu interfered in a match between Tribe Vanguard (YAMATO and KAI) and MaxiMuM (Naruki Doi and Kaito Ishida), while also claiming to be the next challengers.

On July 21 at Kobe Pro-Wrestling Festival, Eita and Shimizu won the Open The Twin Gate Championship by defeating Tribe Vanguard (KAI and YAMATO) and MaxiMuM (Naruki Doi and Kaito Ishida) in a three-way match.

Three days later, BxB Hulk was revealed as the Red Masked Demon, after turning on YAMATO defecting from Tribe Vanguard to join R.E.D.

[48] On June 27, at Muta The World, the group was revealed to be the Los Perros del Mal de Japón, afterwards Eita along with Nosawa and Yo-Hey defeated Stinger (Yoshinari Ogawa, Seiki Yoshioka and Yuya Susumu).

Afterwards, the group started a brawl between the two stables, with Kotaro Suzuki and Ikuto Hidaka coming to help, outnumbering Stinger and getting the upper hand on them.

failed to win the Open The Twin Gate Championship in a three-way match involving Hyo and Kento and D'Courage (Dragon Dia and Yuki Yoshioka).

On March 13 at Great Voyage in Yokohama, Eita defeated Daisuke Harada to win the GHC Junior Heavyweight Championship for the first time.

[50] The following day, Eita made his last match for the promotion, teaming with his Los Perros del Mal de Japon stablemates in a no contest against Stinger.

On May 5 at Dead or Alive, Eita, Rongai and Kotaro Suzuki defeated Naruki Doi, Kaito Ishida and Kota Minoura to win the Open The Triangle Gate Championship.

Later that month, Eita and Los Perros del Mal de Japon made a surprise return to NOAH, attacking Stinger members Chris Ridgeway, Yoshinari Ogawa, Seiki Yoshioka and Yuya Susumu, during a title match for the GHC Junior Heavyweight Tag Team Championship, before nominating them as their next challengers to the Open The Triangle Gate Championship.

On November 23 at Noah the Best, after concluding their feud with Stinger's Yoshinari Ogawa, Nosawa Rongai decided to disband Los Perros del Mal de Japón, due to his eminent retirement from professional wrestling on February 21, 2023.

[51] On December 23 2022, Eita was announced as Yoshinari Ogawa's partner to challenge Kzy and Yo-Hey for the GHC Junior Heavyweight Tag Team Championship at NOAH The New Year on January 1, 2023.

At the event, Eita and Ogawa defeated Kzy and YO-HEY to win the GHC Junior Heavyweight Tag Team Championship.

Despite holding the GHC Junior Heavyweight Tag Team Championship with Ogawa, the two remained distant and their relationship quickly turned soured, as Ogawa turned on Eita after they lost the GHC Junior Heavyweight Tag Team Championship to Tadasuke and Yo-Hey on April 16 at Green Journey in Sendai.

[54] Afterwards, Ogawa announced that he, Chris Ridgeway and Daga were the "new Stinger" and that Eita and Hayata where not considered members anymore.

On May 14, Pro Wrestling Noah held a press conference, officially announcing that Eita had signed with the promotion.