Name of korean rapper and song?

Back in 2009 I found this song that I really liked but I can't remember the name or rapper. The mv started with a guy is playing an invisible piano and everything was all colorful. Then a small holographic girl came up on his right side singing the chorus. The only part of the song I remember is when he says "sarang sarang sarang" and a little pink heart comes up. Please I need to figure out who did this mv!