Moon Byul lives a quiet life with her little daughter Whee In after her wife passed away. Then one day, she meets a woman who is very similar to her late passed wife lost in the woods, but the mysterious woman doesn't have any memories.

Kim Yongsun is a girl who suffers from a rare genetic disease that is incurable, called Xeroderma Pigmentosa A.K.A 'XP'. This disease prevents her from getting out in daylight, because the ultraviolet rays of the sun cause burns to her skin and ill to her health.