The strongest man, possessing numerous psychic powers such as teleportation, telepathy, psychokinesis, clairvoyance, and apport (exchanging items of equal value). He loves sweet desserts, especially coffee jelly. He loathes bugs, particularly cockroaches. His catchphrase is "Yare yare." Despite the beauty of Teruhashi, the top beauty in the series, he never gasped in awe—except for exactly once in Season 2 (or "Thought it was over?"). He's incredibly handsome (likely inheriting his mother's genes). He is 16 years old (2nd year of high school in Japan). Thanks to his overly affectionate parents, he lives a draining life. He is popular with girls (Kokomi Teruhashi, Mikoto Aiura, Imu Rifuta, Chiyo Yumehara, etc.). He hates Kusuke.

Saiki Kusuo's mother. Although she is 37, her skin age is said to be in the 10s or 20s (a beauty). She is kind and pure, but terrifying when angry... She calls Kusuo "Ku-chan" and Kusuke "Ku-ku." She is completely head-over-heels for her husband, Kuniharu.

An ordinary family man working at a publishing company... but at home, he's often treated like a nuisance. Still, he is completely smitten with his wife, Kurumi (they often argue over who loves the other more). He frequently feels ignored by Kusuo and Kusuke. He occasionally calls Kusuo "Kusuemon."

Saiki Kusuo's older brother. A genius who has lost every duel he challenged Kusuo to since childhood. He is currently studying abroad in England, having earned his Master's and preparing for his Doctorate. Note: He is incredibly handsome (inheriting his mother's genes).