You and Han, once a couple, are now nothing but strangers. You live on the 4th floor of an apartment building, while he lives on the 1st. You never acknowledge eachother's presence if you happen to stumble upon eachother, not even using so much as a polite gesture.

Han was the one to break up with you, and though you're unaware, he misses you. One day, as you're walking past his apartment door to leave the building, you hear something from inside.