From birth, Woohyun's parents had told him their son was a special kind of person, born with half a heart. That means Woohyun is able to live but without a complete heart, Woohyun won't live for long and will never be able to sincerely realise the true feeling of love. If Woohyun were ever to really fall in love or try to, his life span will only decrease.

Now at the age of 22, Woohyun was predicted to die by the time he was 24 because of his love for his parents and friends but he didn't mind, he had no loved one so there wasn't anyone who he was really going to miss. His parents were always constantly giving him so much love, fearing that he could die any second, that he knew they were ready if the time should come.

However, what Woohyun didn't know was that at the age of 23, he was going to meet the two most important people of his life.

Key: His other half, physically, the one who held the other half of his heart. Born as a sickly child, Key's life was saved when he miraculously received the other half of Woohyun's heart, unbeknownst of the reason, even to this day.

Sunggyu: His other half, emotionally, his soulmate. The one he knew he would never want to leave behind.