There were two girls who were born in October. They had same birthday and were raised in the same village and in the same class. One led a happy life with loving parents and a brother. Her name was Yoon Eunseo. However, the other was raised by a single parent and was living in poverty. Her name was Choi Shinae. One day Eunseo has a car accident and by a blood test it is found that Eunseo and Shinae were swapped at birth. Girls were returned to their original places. Eunseo's brother Yoon Joonseo is especially confused and saddened by this. Some years later, Choi Eunseo and Yoon Shinae bump into each other at hotel. Eunseo is a poor worker and Shinae is a hotel manager. Meanwhile, Joonseo has become an artist and has a fiancée. One day he's introduced to his friend's girlfriend, and she was his long-lost sister, Eunseo. Now all the relationships start to twist around and Eunseo and Joonseo's sad love begins.

Beautiful Days is a 2001 South Korean television drama series starring Lee Byung-hun, Choi Ji-woo, Ryu Shi-won and Lee Jung-hyun. It aired on SBS from March 14 to May 31, 2001 on Wednesdays and Thursdays at 21:55 for 24 episodes.

Hae Jung is the eldest of four sisters, and is kind and giving to her younger sisters - even though she's actually their half-sister. In contrast, second sister Yu Jin is ambitious and straightforward, and cares deeply for family friend Young Hoon, causing plenty of problems for everyone else! Third sister Yu Mi is materialistic and gets engaged to a rich gentleman despite having another, more suitable lover. And fourth sister Yu Sun is a high school student with a heart problem - and ardent love for her high school teacher! As the years pass, each sister struggles to find true love, and conflicts and difficulties arise. But through it all, they remain true to each other.