5000 years ago, the Kaiju Eugenicists, with Gauma being one of them, brought fortune to a certain country through the use of their power to control Kaiju. They were known as "dragon controllers" to the neighboring country. Juuga used to look up to Gauma as well. The princess of their country became interested in the power, but then the Kaiju Eugenicists were betrayed by the country, while also betraying the country themselves. Gauma, having shifted his loyalty to the princess over his comrades, killed them and then fell over, and seemingly died, gaining the scars on his face in the process.
5000 years later, Gauma and the Kaiju Eugenicists were revived in the modern day. They now consider Gauma to be a traitor for piloting Dynazenon to fight against their Kaiju.
The Kaiju Eugenicists were behind the attacks of Shalbandes and Greyjhom before they revealed their presence to the Dynazenon pilots, and branded Gauma a traitor. Juuga wondered how Yomogi Asanaka, Yume Minami and Koyomi Yamanaka were able to pilot Dynazenon, a supposed "Kaiju" in their perspective, and started to wonder if they were Kaiju Users like them. Later on, Juuga went to Fujiyokidai High School where Yomogi and Yume were studying to look for the boy, to ask him what happened to Gauma that made him betray them, but Yomogi had to go off to work. Juuga considers recruiting the three of them as fellow Kaiju Users.
After Garnix's defeat, Juuga left the team to find Gauma and apologize but Gauma didn't want to hear any of it and started to beat him instead. Disappointed, Juuga left. Juuga and the other three Kaiju Eugenicists attempt to use Instance Domination on Gagula, but realize Sizumu is inside. They allow themselves to be devoured by Gagula for it to power up into its second form. However, they still lose to Gridknight and Dynarex. The Kaiju Eugenicists are destroyed along with Gagula.
- Instance Domination (インスタンス・ドミネーション Insutansu Dominēshon): An ability that puts a Kaiju under his control, and makes it grow to giant size.
- Juuga bears some resemblance to Masayoshi Oishi, which even the singer himself has noticed. The official SSSS.DYNAZENON Twitter account also retweeted his noticing of it.
- Juuga's vision started to deteriorate later in his life, which is why he wears glasses when revived in modern times.