[6] As a child, he competed nationally in the under 40 kg class, and had lost to future teammate Naohisa Takato, finishing fifth place.

He lost to Tural Safguliyev, when the Azerbaijani threw him for ippon in the final, therefore making Nagase settle for silver.

He beat Keita Nagashima in the final to represent Japan at the 2014 World Championships in the half-middleweight category, and claim gold.

Nagase also participated in the prestigious Open category in Tokyo, where he surprised heavyweight opponents by beating Kazuhiko Takahashi, who outweighs him by 40 kg, in the quarter-final.

He was playing ippon judo in his first three fights, however again lost against eventual world champion Tchrikishvili in the quarter-final by shido.

He narrowly won the repechage against Lebanon's Nacif Elias by shido, but was defeated by Pietri in a revenge match by waza-ari, leaving Nagase to finish fifth place.

With Russia President Vladimir Putin watching and the home crowd cheering, the Russians capitalized on their advantage and defeated the first two Japanese judokas.

Nagase managed to overcome the pressure and defeat Murat Khabachirov with an ouchi gari for ippon, salvaging Japan's chances.

On the course to the final, Nagase was against double world and Olympic champion Kim Jae-bum in the quarter-final, and defeated him by waza-ari.

- Nagase's comment on his junior's blog post, thanking his alma mater [24] Nagase made a shock exit in the second round of the Grand Prix in Düsseldorf, losing to Belarus' Aliaksandr Stsiashenka by ippon and waza-ari.

Nagase again won the gold in the half-middleweight category at the national championships, beating Nagashima for the second time.

Nagase played ippon judo in his first two fights, however narrowly won by shido against Egypt's Mohamed Abdelaal.

He defeated Pietri in the final with a sankaku kami shiho for ippon, making newaza one of Nagase's most effective techniques.

The referee appeared to be pressured by Lee's coach Song Dae-nam, who was avidly shouting for disqualification.

Nagase had been knocked in the mouth during the fight, and was bleeding, but did not seek medical attention until after the final decision had been called.

Japan's head coach Kōsei Inoue later on explained that Nagase was holding the judogi, and not the leg.

"[32] Nagese went on to win bronze against Greece's Roman Moustopoulos, scoring an ippon, a waza-ari and two yukos.

[33][13] By winning the national title, and being the highest ranked Japanese in the half-middleweights, Nagase was chosen to represent Japan in his division at the 2016 Olympics.

[34] Nagase returned to international competition after a five-month absence at the Grand Slam in Baku.

De Wit managed to catch the Japanese off guard, scoring a waza-ari a minute and a half into the fight.

Nagase faced Bulgaria's Ivaylo Ivanov in the final, and defeated him in 40 seconds by ippon with kosoto gari.

After several tries on the ground, Nagase finally had a breakthrough with kouchi gaeshi for yuko which he connected to tate shiho gatame for ippon.