Sequel to MSG from twin sister's POV
I have never read or heard any comments by director Kwak, but I was surprised that noone here has mentioned that it could be quite possible that Kyung-Jin and the nameless girl from My Sassy Girl are twin sisters. (Sorry if this has been already discussed - I have read most of the threads, but not all.)
That would also explain why Kyung-Jin has a photo of the MSG girl on her piano, because that would be her beloved dead twin sister.
Starting from this point Windstruck then would be a sequel to MSG from the twin sister's (Kyung-Jin's) perspective. Since MSG and Windstruck are three years apart, Kyung-Jin's twin sister might have tragically died in the meantime.
It would then also explain Cha Tae-Hyun's perplexed, strange look on his face in the last scene - he is seeing a woman who looks exactly like his deceased girlfriend.
Since I found Windstruck painfully boring and all the gags contrived and overdrawn, I didn't pay too close attention, so I could be totally wrong with my sequel theory. But it probably holds up better than all the implausible prequel-theories.
Any thoughts?