Kusuke Saiki, older brother to Kusuo Saiki, was born June 16 with striking blonde hair and eyes slightly darker than his parents’, defying their genetic expectations. A prodigy with an IQ of 218, he earned a PhD from Cambridge University by age 14. His childhood rivalry with Kusuo, marked by repeated losses despite relentless effort, sparked a lifelong obsession to surpass his brother. Their dynamic blends calculated teasing and subdued camaraderie, with Kusuke insisting his provocations stem from amusement rather than malice. Kusuke’s inventions shape pivotal moments in Kusuo’s life. In middle school, he collaborated on the power-suppressing devices his brother wears. Later, he engineered a "Telepathy Canceler" to obstruct Kusuo’s mind-reading abilities, though he instinctively deciphers his brother’s intentions. His technological feats include a functional time machine, which he deployed to navigate a parallel universe where Kusuo perished, and planetary defense systems capable of neutralizing apocalyptic threats like Earth-destroying meteors. Prideful, manipulative, and harboring a sadistic streak, Kusuke orchestrates chaos for entertainment—observing Kusuo evade frenzied crowds or dismissing Kokomi Teruhashi’s infatuation with detached indifference. He demonstrates selective loyalty, refusing to implicate his mother in false accusations while largely disregarding his father. In *The Disastrous Life of Saiki K.: Reawakened*, Kusuke destabilizes Kusuo’s existence by providing a limiter that temporarily nullifies his psychic powers, compelling him to navigate ordinary life. This intervention underscores Kusuke’s dual influence as both disruptor and unintentional mentor. Manga-exclusive arcs further cement his reality-altering capabilities, depicting his creation of a Kusuo-free parallel universe and high-stakes interventions that manipulate existential outcomes. Kusuke’s motivations remain anchored in intellectual domination over his brother, yet sporadic acts—like ensuring Kusuo’s survival during crises—hint at veiled concern. This paradox positions him as a mercurial neutral force, leveraging genius and emotional ambiguity to propel consequential plot developments across adaptations.