Kuusuke Saiki, the exceptionally intelligent older brother of Kusuo Saiki, lacks psychic abilities but received significant parental focus until Kusuo’s birth shifted attention, igniting intense sibling rivalry. This dynamic drives his persistent technological inventions aimed at surpassing Kusuo, including devices to suppress psychic powers. Resentment fuels his actions, rooted in Kusuo’s innate abilities overshadowing his achievements. He displays intellectual arrogance, dismissing most humans as inferior while showing occasional care for family members—excluding his father. His lack of empathy extends to viewing ordinary lives as disposable. Rare moments, however, hint at a complex, nearly friendly rivalry beneath the antagonism toward Kusuo. After moving to England at fourteen, he became a Cambridge University doctoral candidate. There, he invented a "telepathy canceler" to block Kusuo’s mind-reading, demonstrating technical ingenuity against psychic powers. He once challenged Kusuo to high-stakes London hide-and-seek, leveraging Kusuo’s friends in a scheme that failed when time expired, intensifying his fixation on defeating his brother. His actions include emotionally distressing Teruhashi Kokomi—making her cry despite acknowledging her beauty—which caused unforeseen repercussions. Later, he escalated rivalry by kidnapping Kusuo’s friend to lure him into a confrontation, deploying a custom-built mecha. Post-graduation, he relocated to his grandparents' home, indicating partial withdrawal from direct conflict but retaining competitive drive. His portrayal remains consistent: a genius antagonist whose inventions and schemes challenge Kusuo, reflecting unresolved envy and intellectual arrogance.