Suzu Hagimura

Height: 140.6 cm
Weight: 31 kg
Age: 16 years
IQ: 180

A first-year, 15-year-old (16 later in the manga) genius return student who serves as the Student Council Treasurer, and is the most mentally mature of the characters, however she is very sensitive about her body, which still appears to be that of an elementary school student. Many of the jokes involving her focus on her childish appearance or lack of height which cause her to fly into a rage whenever it is mentioned. Another running gag is her extreme fear of the paranormal, which often leaves her shivering and shaking in fear. She is the smartest student at Ousai Academy and boasts an IQ of 180. She can also perform 10-digit calculations in her head.

(Source: Seitokai Yakuindomo Wiki)