Kairen emerges as the primary antagonist in *Shinkansen Henkei Robo Shinkalion THE ANIMATION*, debuting in Episode 40. He rules the Kitoralsus, orchestrating monster attacks across Japan after the mysterious Black Shinkansen appears. Commanding subordinates like Torame and Sougyoku, Kairen directs assaults against humanity, compelling the Shinkansen Ultra Evolution Institute to deploy child-piloted Shinkalion units in response. Key confrontations unfold in Episodes 61 and 74, culminating in his initial defeat by the united Shinkalion drivers.

Despite this setback, Kairen resurfaces in expanded franchise media. He returns as the central antagonist in the novel series *Shinkansen Henkei Robo Shinkalion Z —The Revived Kairen—*, where his unexpected revival forces the Institute to counter him with upgraded Shinkalion Z units. This narrative concludes the original anime season's continuity. Kairen also appears in the film *Shinkansen Henkei Robo Shinkalion the Movie: The Marvelous Fast ALFA-X That Comes from the Future*, set after the Kitoralsus arc, though his role amid new extraterrestrial threats remains less defined.

His name derives from the Japanese word "zoisite," aligning with a mineralogical theme. Physically, he possesses multicolored hair and yellow eyes. Across multiple timelines and installments, Kairen's actions consistently instigate large-scale conflicts, cementing his status as a recurring existential threat that demands unified opposition from human pilots and their transforming Shinkalion counterparts.