Cha Tae-hyun
In the start of "My Sassy Girl" she is distraught over a boyfriend that died (though the reason was never disclosed) before meeting Cha Tae-hyun, and in "Windstruck" her boyfriend (Myung-woo) died due to hunting Sin Chang-su. The explains why the final scene of "Windstruck" in which Kyung-jin is saved by new soul mate (played by Cha Tae-hyun, the male lead from "My Sassy Girl") on a train platform, is very similar to the beginning of "My Sassy Girl", essentially setting up "Windstruck" as a spiritual prequel to "My Sassy Girl".