Leap Day

Born on the day and night of February 29, Day and Night are each plagued by a terrible curse that, every four years, will take from them the person they cherish most.

The danger the curse poses to those around them keeps the two isolated. One day, Night meets Dream and she becomes his source of joy. Meanwhile, Day finds himself caring for Ozone, the autistic son of a distant relative following her death. As their twentieth birthday approaches, Day and Night's fears for their loved ones mount.

(Source: MyDramaList)