This is the original version of Princess Knight that was serialized in Shojo Club from 1953-1956. The 1963 version, serialized in Nakayoshi was completely redone from the ground up.

Set in a medieval fairy-tale type setting, this is the story of young Princess Sapphire. When Sapphire is in heaven waiting to be born, a mischievous cherub named Tink accidentally gives her a second heart, and the young girl is born with both the brave and adventurous blue heart of a boy, as well as the loving and caring red heart of a girl. Realizing a mistake has been made, God sends Tink to earth with instructions to retrieve the blue boy’s heart. However, Princess Sapphire has been born into the Kingdom of Silverland, where only a male heir can inherit the throne, so retrieving the boy’s heart is no easy task. In order to keep the evil Duke Duralumin from becoming next-in-line to the throne, the king and queen announce that a prince has been born – forcing Sapphire into a life of deception. Sapphire was inspired by the Takarazuka Revue all-female theatre troupe, of which Tezuka was a long-time fan.

Frequent misconceptions (largely from American based or other such sources) place Princess Knight as the first Shojo Manga ever made. Shojo manga has existed for as long as manga itself. Some examples being Katsuji Matsumoto's Kurukuru Kurumi-chan from 1938 and Shosuke Kurakane's Anmitsu-hime from 1949 in addition to a myriad of others.