“Through the Night” (밤편지, bampyeonji — “night letter”) is IU's 2017 lullaby-like love song. She writes to someone at night, too shy to say it in person: she'll send the light of fireflies to their window, she hopes they sleep well, and she wishes she could tell them how much they mean to her.
IU, one of Korea's most loved singer-songwriters, released it with just an acoustic guitar and her soft voice. It topped Korean charts and became one of her signature songs.
It's an ideal first Korean song: slow, quiet, and full of gentle everyday vocabulary — night, letter, window, to sleep, love. Listen for the polite verb endings (-요), which make the letter sound warm and respectful.