"It's Christmas Day" was composed and written by Kim. After taking over spring with "Bom Bom Bom", summer with "Love Love Love", and autumn with "Home", Kim filled all of four seasons with his winter song release. On December 11, 2014, Kim posted up on his official Instagram account, stating "It's gonna be Christmas Day soon. Wait for it. Recording a new song."

The self-penned single was released on December 19, one day ahead of his year-end concert, "Our Winter #2". Its music video also was revealed at the same day, bringing all kinds of Christmas feels with Kim sweetly singing while playing the piano and guitar. "It's Christmas Day" peaked at number 27 on the Gaon Digital Chart, having sold over 69,000 digital copies as of January 3, 2015.

Following its release, Kim performed the song at Mnet's M! Countdown broadcast on Christmas Day of that year.

All tracks written by Kim Sang-woo.

Credits are adapted from the liner notes of the single's limited CD edition.

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Wikipedia