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.
Sizumu somehow entered the same school and the same class where Yomogi Asanaka and Yume Minami were studying in, posing as a transfer student. When the chance arose, he asked them to bring out Dynazenon despite them being unable to because no Kaiju were around anyway. Sizumu later talked to Yomogi and Yume about the nature of Kaiju, disclosing to them ta the Eugenicists didn't create the Kaiju; they would be born anyway from the desires of humans, and that they simply wanted to create a world where Kaiju were "necessary".
Suspiciously, Sizumu was not seen to disappear during Garnix's attack, nor was he or his corpse present in the "past" when Gauma fought the Kaiju Eugenicists.
After Garnix's defeat, Sizumu suddenly left Fujiyokidai High School. Soon, Yomogi confessed that he liked Yume and before she could say anything, they were ambushed by Sizumu, who revealed that he had been following them around to feed off their emotions. He tried to attack them but Gauma got in the way, almost getting killed. Sizumu then defeated Knight and unleashed Gagula to destroy the city. While Yomogi, Yume and the 2nd take care of Gauma, Knight fought Gagula as Kaiser Gridknight but lost. Yomogi and the others then went to retrieve their parts of Dynazenon to pilot together for the last time. Even with their teamwork, they were still being overwhelmed by Gagula until Yomogi used Instance Domination on it to force it to move its mouth up and provide the others with an opening to attack. While doing so, he had a conversation with Sizumu inside Gagula, where he was asked why he wanted to waste his powers as a Kaiju User and therefore his ability to free himself from the world. Yomogi stated that he would rather live as a normal human through the ups and downs of life along with the bonds he made with his friends. Sizumu is unable to comprehend him and leaves. With everyone's efforts, they manage to defeat Gagula and the Kaiju Eugenicists.
- 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. He can use this ability on himself to release his Kaiju, Gagula.
- Kaiju Empathy: An ability unique to himself, Sizumu can precisely feel the thoughts of the Kaiju he interacts with.
- Gagula: Sizumu has the Kaiju Gagula growing inside him. The Kaiju grants him powers as well.
- Shockwave: A repulsive wave that can easily send a full-grown man flying.
- Barrier: A barrier used to block attackers.