Kdrama characters

Which Kdrama has the best characterdevelopment in your opinion and what character/characters? ^^ It can be a good and a bad change, but the character has to go through some kind of development and become like a "better/worse" person. I know that a lot of Kdramas have those kind of characters, it's difficult not to have that, but which Kdrama and character do you think has changed the most through-out the drama? :D My pick: Kimura Shunji from Bridal Mask ^^ Here is no doubt there that that character went through an huuuuge characterdevelopment, *SMALL SPOILER FOR THOSE WHO HAVEN'T SEEN BRIDAL MASK* going from the sweet teacher to become a yeah......revenge-thristy "beast" I guess you could say xP (Loved him through-out the entire story too though). *END OF SPOILER*

Lee Cho In (So Ji Sub) in Cain and Abel as I was satisfied that he became a strong person to get his revenge altough he was a kind heart in the begining and change to a confused and weak person in the middle.

SPOILER ALERT:
I think Harry from Missing You became completely twisted because of fear - he is the product of a corrupted system of greed that he was unfortunate enough to be born into ): I truly cry for his character, after he committed a murder when he was 12 (all because he was afraid and trying to defend himself), he became worse and worse to the point where his inability to cope with his loss of his mother resulted into his becoming a dysfunctional adult - the writer of the drama really did a good job with his character as the bad guy: the director presented Harry as a vulnerable child, his desperation that triggered self-defense, and his childish greed that he never grew out of so he ended up a vengeful adult that the viewer can't help but pity

Harry going Loco in the Coco, if you catch my drift ;)

Best character development: Queen Seon Duk - Mi Shil and Duk Man (in this drama only you maybe fall in loved with evil character :D ).