Huh?

The whole story of Here U Are is about YuYang telling their story, as how they met each other and all. The Valentines Special is a little forward than that, after they were already together as a couple.
Have you watched "How I met your mother"? Same thing, there is a great advantage in that kind of narrative, you can fast forward and back a lot, because the main point is to connect the dots little by little.
DJun also use some spoilers in the story to keep the viewers' attention and engage them in the story as it flows.

AWESOME !!! Thank you!!!!