While studying, Nagai started competing in amateur shootboxing and amassed a 5–2 record, which made him change his ambition, so after graduating he went to join UWF Newborn instead of AJPW.

He competed in a number of shoot contests during the early years of RINGS where he was defeated by Dick Vrij on May 16, 1992, by TKO, and would also lose to Willie Peeters on July 16, 1992, however he got notable KO victories against Koichiro Kimura and Nobuhiro Tsurumaki, and a decision win against Nobuaki Kakuda.

In 1994, Nagai looked to ascend the scale by taking part on the Mega Battle Tournament 1994, eliminating Ameran Bitsadze on the first round, but then losing to Chris Dolman in the second.

He then got another MMA victory against Willie Peeters, winning via heel hook, but his momentum got cut short by a submission loss to Kiyoshi Tamura at the Mega Battle Tournament 1996.

In the 2000 Young Generation Battle, Nagai went undefeated for the entirety of the tournament, beating Usuda, Mohammed Yone, Mach Junji, Rastaman and Minoru Tanaka to reach the final, where he lost to Alexander Otsuka.

Almost immediately after Battlarts began its hiatus, Nagai was announced for the 2000 Real World Tag League in All Japan Pro Wrestling (AJPW), the promotion he had originally hoped to join in high school.

[8] Nevertheless, Nagai's position as a loyalist in the post-exodus era All Japan continued to rise, and he teamed with Toshiaki Kawada in a loss to TenCozy (Hiroyoshi Tenzan and Satoshi Kojima) on September 16 on an NJPW card.

[9] Nagai teamed up with Kawada again for the 2001 Real World Tag League, seeing much greater success than the previous year, earning 10 points and making it to the final where they lost to Keiji Mutoh and Taiyo Kea.

[14] In July, Makai #5 and #4, who had dubbed themselves Halimao'z (破悧魔王'Z, Harimaozu, "Devil Demon King'z"), challenged for the IWGP Tag Team Championship, losing to reigning champions Hiroshi Tanahashi and Yutaka Yoshie in Osaka.

[15] Nagai competed at Wrestling World 2004, teaming with Makai #1, Ryushi Yanagisawa and Ryota Chikuzen to defeat the Crazy Dogs (Enson Inoue, Hiro Saito, Michiyoshi Ohara and Tatsutoshi Goto).

[16] Nagai would compete twice at NJPW's King of Sports pay-per-view in March, first teaming with Shibata, #1 and Yanagisawa to defeat Blue Wolf, Shinya Makabe, Toru Yano and Yutaka Yoshie, but later losing to Josh Barnett in a singles match.

[18] It was also during this time that he aligned himself with fellow Rings alumni Masayuki Naruse, with the two unsuccessfully challenging Genichiro Tenryu and Masanobu Fuchi for the All Asia Tag Team Championship on July 26.

After leaving New Japan, Nagai debuted for Dramatic Dream Team (DDT), choosing a lighter schedule in a comedy promotion which would allow his injury to heal at a quicker rate.

It was in MUGA Nagai would find his new home, competing regularly for the next few years while also making occasional appearances in DDT and various shoot style promotions such as Battlarts and Daisuke Ikeda's Fu-Ten.

[29] Nagai would later debut and make Pro Wrestling Noah his home in late 2017, entering the 2017 Global League where a loss to Naomichi Marufuji stopped him from reaching the final.