Diversely-limited
In EP 14.,

miraee:

Towards the end, between Jaehun and Taehee’s phone call convo, what’s the song Byunggun is singing? I forgot which episode, but Byunggun and Taehee previously sang the song also as a duet. The song sounds so familar, like it’s from the Phantom of the Opera. But I’m not sure. I really need to know.

It’s the same song as in Ep12 when Taehee was singing to Agency’s Manager and his friends, and then Byung Gun continues the song…singing to the red-track-suit ghost. I get the audio rip from here…

http://www.dramabeans.com/2012/01/whats-up-episode-12/

and yeah I’m not sure, but some said the song is from the English version of It’s Not Goodbye from Laura Pausini