While Zico is a bad boy who involved himself in fights, yet at the same time a charmingly handsome one with lots of fangirls, Shin Hye is the polar opposite,  just an ordinary girl who led her life quietly until Zico budged in.

Zico

The usual badass boy (The KingKa) you could expect from any school in Seoul except that this one was only much hotter, more egoistic, and much 'badder' than any other boy you could find off the streets.

Park Shin Hye

She was an ordinary girl, with ordinary looks and ordinary brains. The only thing that wasn't ordinary about her was that she didn't fangirl over Zico like every other ordinary girl did. 

Park Kyung (comes in at the later chapters)

He likes Shin Hye but he only gets friendzoned in the end.

Block B

Zico's Buddies.