It totally IS a fairy-tale, since the pieces of puzzle put together are utterly unrealistic... BUT if supposedly it ever once HAPPENED so - or it might ever happen, the outcome is marvelous. There is this retarded father who falls victim to a cruel society, the compassionate guardian who hasnt always been like this, the cellmates who are more humane than the people outside, and - of course - the brilliant daughter played by an impressive CHILD ACTOR... Just these and it's enough to have a unique movie, brilliantly played by everyone, from main actors to supporting cast.
What we can see here is not just a moving story, but also a top product of the drama-school of Korea. You know, when it's too good to be true...