Jun Pyo ♥ Jan Di
Jan Di initially hates him and his two friends, Yi Jung and Woo Bin. She is the only one who is strong enough to stand up against Jun Pyo after he tries to humiliate Min Ji, Jan Di's only friend at the school. Jun Pyo then puts a red card in Jan Di's locker which indicated that she was a victim for F4. After continuous bullying his feelings for Jan Di begin to develop.
However, Jan Di dislikes him for what he had done to her and she already has taken a liking in Ji Hoo (although she believes she likes him, she later finds out it is just a friendly like). Jun Pyo persists in making Jan Di fall for him and succeeds. As their relationship becomes official, Jun Pyo's mother becomes an obstacle. She does everything possible to prevent Jun Pyo from being with Jan Di. Later on Jun Pyo gets hit by a car and remembers everything except for Jan Di. A crippled girl, named Yumi, who is at the same hospital with Jun Pyo, comes into the story and befriends Jun Pyo. Yumi and Jun Pyo hosts a pool party, saying that they are going to go overseas to the U.S. to study. Jan Di, desperately trying to get Jun Pyo to remember her, shows Jun Pyo the necklace he gave her and throws it into a pool. She asks him if he knows how to swim. Then Jan Di jumps into the pool and Jun Pyo's memory is triggered and rescues Jan Di.
Jun Pyo realizes his inner blackness in episode 5 and thinks Jan Di, which translates to "Grass" in English, really represents his true love.
Ji Hu ♥ Jan Di
When Jan Di was being bullied after receiving the red card, Ji Hoo was the only one who offered her consolation. Such generosity made Jan Di seem to develop feelings for the soft-spoken Ji Hoo. However, his first love was Seo Hyeon, a lawyer and a model. He even followed her to Paris, as So Hyeon went back to Paris. While he was gone, Jun Pyo took action on Jan Di and she ended up liking him too. But when Ji Hoo came back, Jan Di was in a state of confusion, not knowing who she really likes. Eventually, Jan Di comes to an understanding of her feelings and chooses Jun Pyo. At New Caledonia, Ji Hoo comes somewhat begins to like Jan Di and this develops throughout the TV series.
Yi Jeong ♥ Ga Eul
Ga Eul is Jan Di's best friend since kindergarten. Ga Eul starts developing romantic feelings for Yi Jung after he helps her get over her boyfriend who just played with her. At first, it's obvious that Yi Jung only thinks of her as a good friend. Ever since Ga Eul helps him through his self-destruction, Yi Jung finds out that Ga Eul, not Eun Jae has always been by his side. He eventually shows some feelings towards her, especially when he promises to visits her first by the time he comes back from Sweden.