Lee Kyung-Min (Kim Rae-Won)
In many ways university student Lee Kyung-Min still acts immature. His bad financial situation forces him to move into the rooftop apartment with Nam Jung-Eun. First he chases after the wealthy Na Hye-Ryun who doesn't share the same feelings he has for her. Suspecting that Jung-Eun is pregnant, he starts to pay more attention to his studies in order to provide a better future for her and her unborn child. He is envious of the wealthy Yoon Dong-Joon who attracts women easily and even starts to fight with him after he sees him and Jung-Eun together.

Nam Jung-Eun (Jung Da-Bin)
Nam Jung-Eun, the female protagonist of the series, aims to start an independent life by seeking her own home and means of survival. At first she is not at all interested in Lee Kyung-Min, the guy with whom she is forced to share her rooftop apartment. However, after a while she gets used to his company and would like to get to know him better. Regrettably, this idea is hindered by the fact that Kyung-Min still longs for his old love interest Na Hye-Ryun and Jung-Eun also starts to draw the attention of her boss Yoon Dong-Joon.

Yoo Dong-Joon (Lee Hyun-Woo)
Wealthy Yoo Dong-Joon is the director of an ad agency for which he solves all important business matters. More mature than Lee Kyung-Min, he is the constant desire of many women. Na Hye-Ryun is especially taken with his good looks and good financial prospects. However, he is not interested in her. Everything changes after he gets to know Nam Jung-Eun. But as fate would have it, Jung-Eun is not attracted to him but to the ordinary Kyung-Min...

Na Hye-Ryun (Choi Yoon-Jin)
Na Hye-Ryun is the pampered girl of a wealthy family and her beautiful looks turn her into a subject of desire for Lee Kyung-Min. However, she is not at all interested in him but has a crush on the rich and good-looking Yoon Dong-Joon. She is totally envious of Nam Jung-Eun who wins the favor of Dong-Joon and also cannot bear the fact that Kyung-Min lives together with Jung-Eun. Unhappy about her own life she tries to sow discord whenever and wherever she can.