Yoo, Jae-Hee

The younger brother of Yoo Da-Hee and Yoo Na-Ri and the third of four siblings. Like his older sister, Yoo Da-Hee, he appears to be good at studying. He then says that if he wants to be like his older sister, this much is natural, but he seems to be a little worried about this, similar to his younger older sister, Yoo Na-Ri.

(Source: Namuwiki, translated, edited)