I really liked the fourth OST, ‘The One Person Who Filled Me’!

"The One Person Who Filled Me" is characterized by a warm acoustic folk sound, capturing the sincere feelings toward the one person who unwittingly seeped into the protagonist's weary life and became a source of comfort. The lyrical yet melodic arrangement, harmonizing with Seo In-guk's voice, really creates a great atmosphere. You definitely have to give it a listen!