Kūsuke Saiki, the older brother of Kusuo Saiki, lacks psychic abilities despite his younger brother possessing them. This sparked an intense competitive rivalry from childhood, where Kūsuke constantly challenged Kusuo only to consistently lose due to his brother's powers, fueling a deep obsession with surpassing him. Possessing genius-level intellect, Kūsuke left Japan at 14 to become a doctoral candidate at Cambridge University. Abroad, he dedicated himself to inventing devices specifically designed to counter Kusuo's psychic abilities, reflecting his enduring fixation. A significant creation is the "telepathy canceler," which prevents Kusuo from reading his thoughts. After graduating, Kūsuke returned to Japan. He chose to live with his maternal grandparents, Kumagoro Saiki and Kumi Saiki, rather than his immediate family. Kumagoro exhibits a tsundere personality, while Kumi maintains a youthful demeanor and fashion sense. Kūsuke's character is defined by intellectual arrogance, narcissism, and a relentless drive to outwit his brother. This compels him to create elaborate schemes and technologies aimed at proving his superiority, though these efforts typically end in failure. His motivations stem from envy of Kusuo's innate powers and frustration at his inability to defeat him through conventional or scientific means.