A bad dragon kidnapped a princess but was beaten by a just knight. The knight rescued the princess and they lived happily ever after. "Well, this used to be true in my father's day" said the good-natured dragon, who had no interest what so ever in attacking humans. One day, he met a princess and fell in love with her, but a bad knight kidnapped the princess. What a terrible thing to happen! The just dragon went to conquer the bad knight and rescue his princess.
In this story, the basic pattern of ordinary tales has been reversed creating a fairy tale of unique charm as a result. The new charm of the story is that you can not distinguish "a good person" from "a bad person" by his appearance. Dragons also have hearts. Through this book, Tezuka Osamu is probably trying to save the dragons that are unfairly treated in so many children's books, like a just knight.