Here are the list of characters: 

Lee Sungmin

A fifteen-year old incoming freshman in high school. He loves his family and friends. He is a talented dancer and does well in his studies. However, his life takes a turn for the worst and it will change him, forever. 

Cho Kyuhyun

A fifteen-year old who helps Sungmin when he falls down. He has no intention of attending high school, but when he helps Sungmin, he is forced to take the entrance exam, and being the genius he is, passes. He doesn't like how his father always pressures him to become a doctor because he never wanted to become one. He later discovers that Sungmin is his classmate. His life changes after his older brother passed away. 

Lee Donghae

A year older than Sungmin, he excels in dancing and is in the same dance club as Sungmin. He is Sungmin's crush. 

Park Jungsoo (Leetuek)

A very caring mother who loves to look after his children. He is Kangin's "wife"  and Sungmin's "mother." He works as a nurse in a nearby hospital and is kind-hearted towards everyone. However, after learning about his son's disease, it is a great shock to him, and he resorts to trying to hide the truth.

Kim Youngwoon (Kangin)

Sungmin's father. He is very over-protective of his children and can be quite scary at times. However, all in all, he loves his family very much and cares about them. He owns the bread shop in which their family lives in. 

Kim Ryeowook

Sungmin's friend since middle school. An energetic, hardworking student, he is also apart of the dance club Sungmin joins when they start high school. 

Henry Lau

An incoming freshman like Sungmin. He befriends Sungmin and Ryeowook when he discovers they are in the same homeroom class and will be in the same dance club with each other. 

Lee Hyukjae (Eunhyuk)

Sungmin's younger brother. He is lazy and doesn't try in school. However, after he is told about Sungmin's condition, he decides to change the way he lives his life. 

Kim Heechul

One of Kyuhyun's friends. He is part of the Biology Club with Kyuhyun and is somewhat of a nerd as he wears glasses. 

Kim Kibum

Another one of Kyuhyun's friends. He is part of the Biology Club with Kyuhyun and Heechul. He has a crush on Ryeowook. 

Hangeng

Kyuhyun's older brother who tragically passed away in an accident. 

Choi Siwon

Sungmin's doctor who is a specialist in Neurology. He tries very hard to help Sungmin and is determined to find a cure to his disease. 

Seohyun

A schoo girl who is in the same year as Sungmin and Kyuhyun. She has a big crush on Kyuhyun and always tries to please him. However, when she insults Sungmin because of his condition, Kyuhyun acts cold towards her, warning her to watch .

Sunny

Seohyun's best friend who accompanies her around. 

Kim Jongwoon (Yesung)

He has the same disease as Sungmin, but unlike Sungmin, he is very pessimistic about living. (You'll learn more towards the end)