Usually I used the character introduction at the beginning of my story but let me do it since we're not yet in the half of the story;

MAIN CHARACTERS:

Lee Donghae; He is the anti-hero of the story, like the protagonist/antagonist in one. He holds a dark secret only he, Minho, and Hyukjae knows who he really is. He is the most trusted friend of Kyuhyun even if they just know each other for less than a year. He had his own motives of making friend with Kyuhyun thre reason: Revenge. Kyuhyun's father is the reason of Donghae's father suicide. And because of that he wants to have revenge by making Kyuhyun suffer financially and emotionally. He is a great Track and Field player, but since he is per-occupied with his goal he left them but still under their scholarship. It's either you and him or pity him because of his reason to live.

Lee Hyukjae: In this story he is a limp guy who had taken a liking to Donghae. He is very forgiving and understanding a lover of music and a doting son to his father. He had an accident when he was a kid but this doesn't stop him from looking at all the positive things in life. Donghae enjoyed his company due to his gentle nature which puts Donghae at peace and made him forget his motive in life. He is one of the center key of the story. He loves music and is very kind.

SUPPORTING CHARACTERS:

Cho Kyuhyun: He is the 2nd son of the owner of Cho bank, he is very kind to anyone. He treasures Donghae as a friend even if they just known each other much to Yesung's jealousy. He can lose everything but not Sungmin as he loves him dearly, He is very much concern of Donghae's welfare which will make him to dislike Hyukjae or Minho because of wanting to protect his friend's reputation. I know he is a different from the evil Kyu we know but I love making him kind ^^.

Lee Sungmin: He is Kyuhyun's childhood love and fiance, he will be one of Donghae's tool for his revenge. A kind hearted person who seems to worried for everyone especially Kyuhyun, but he will be tested due to Donghae's persistance.

Choi Minho: A childhood friend of Donghae who had always admired him, he is worried of his friend's plan and always trying to make him realize right from wrong. He will also be one of Hyukjae's close friend as they share their sentiments with Donghae.

Jung Yunho: A worker at Sungmin's father's company. he will be Donghae's mentor at work and for his revenge. 

Yesung, Choi Siwon and Tiffany: They are Sungmin and Kyuhyun's childhood friend. Siwon is the jokester and the would always give them latest school news. Tiffany is Sungmin's girl-friend like they bond all the time like shopping etc. Yesung is Kyuhyun's best friend but all chnage when Donghae appeared much to his annoyance out of the three Yesung is the most suspecting about Donghae background.

So there you go just a little trivia about the characters