He won the two-minute quarterfinal and semifinal bouts against Tatsuki Kitayama and Koki by decision, and faced Akihiro Kaneko in the finals.
Gunji lost to Tatsuya Tsubakihara in the semifinals by split decision, after two additional rounds were contested.
He beat Kouka Minowa by unanimous decision in the second round, and notched knockouts of Shizuma Nakashima and Issei Ichiki in the quarterfinal and semifinal respectively.
Gunji fought a rematch with Tatsuya Tsubakihara in the tournament finals, winning by unanimous decision.
Takei won by unanimous decision, with all three judges scoring the fight 28-27 for him, thus handing Gunji his first professional loss.
[17] Gunji extended his winning streak to three fights with a unanimous decision victory against Taisuke Degai at Krush 74 on March 3, 2017.
[26] Advancing to the semifinals of the tournament, Gunji faced Tatsuya Tsubakihara for the fourth time in his career at Krush 96 on December 16, 2018.
[28] Gunji met the undefeated Masashi Kumura in the tournament finals, held at Krush 98 on February 16, 2019.
[30] Gunji was scheduled to fight Masashi's brother Shuhei Kumura in the co-main event of Krush 106 on October 13, 2019.
[35] Kumura won the rematch by unanimous decision, scoring a single knockdown in the third round with a well placed knee to the head of Gunji, as the latter was ducking out of an exchange.
[4] He was ranked in the Combat Press flyweight (-56.7 kg) top ten between September 2020, when he peaked at #5, until March 2021, when he moved up in weight.
He was scheduled to make his divisional debut against Yusho Kamemoto at K-1 World GP 2020 Winter's Crucial Bout on December 13, 2020.
He scored the first knockdown of the fight at the 1:32 minute mark of the second round, dropping his opponent with a right straight-left hook combination.
Although Kamemoto was able to beat the eight-count, he was quickly knocked down again with a left hook, prompting the referee to stop the fight.
[44] Gunji was scheduled to face the reigning Krush Featherweight champion Takahito Niimi at K-1 World GP 2021: Yokohamatsuri on September 20, 2021.
[46] Gunji was scheduled to challenge the reigning K-1 Featherweight champion Tatsuya Tsubakihara at K-1 World GP 2021 Japan on December 4, 2021.
[54] Gunji advanced to the penultimate bout of the one-day tournament, where he faced the reigning Krush Featherweight (-57.5kg) champion Shuhei Kumura, who earned his place in the semifinals with a second-round stoppage of Jawsuayai Sor.Dechaphan.
[55] Advancing to the finals, Gunji faced Toma Tanabe, who he had beaten by an extra round decision on April 3, 2022.
[1] Gunji faced the 2022 K-1 featherweight Grand Prix semifinalist Wang Junguang at K-1 World GP 2022 in Osaka on December 3, 2022.
[67] Gunji faced Cristian Bogdan for the vacant ISKA Oriental rules Intercontinental Super-featherweight (-59kg) title at the Japan Martial Arts Expo on October 19, 2024.