The one on the left is Su-ho and the one on the right is Yeon Si-eun.

His appearance is cute; Su-ho is handsome because of his smile, and Yeon Si-eun is cute because of her seriousness and good looks. Su-ho loves to eat, while Yeon Si-eun likes to study. Su-ho doesn't like people who bother others without having done anything wrong, while Yeon Si-eun doesn't like it when people mess with those she cares about. Su-ho hates it when things are hidden from him or when he's lied to, while Yeon Si-eun hates evil people. Su-ho loves to have a good time, while Yeon Si-eun loves to bring justice to evil people. (They fight the bad people from the institute or other places in the city, but Su-ho is more professional.) (Su-ho always sleeps in class, so leave him alone; he works as a delivery driver on his motorcycle.) (Yeon Si Heun almost never smiles, not even a little.)