Following the massive success of Jungle Emperor in Japan, Dr. Tezuka created a sequel in 1966, released locally as The New Jungle Emperor or Onward, Leo! The catch for international audiences was that Tezuka produced this series independently, without an agreement with NBC, and stayed much closer to his original manga narrative. This approach resulted in numerous character deaths and episodes with a somber tone. NBC deemed such content unmarketable and, content with their existing stock of 52 episodes, did not broadcast the New Jungle Emperor series in the United States until 1984, when it aired under the title Leo The Lion.
Set several years after the original Kimba series, this installment features an adult Kimba who is mated to Kitty and has two cubs. The primary focus is on Rune, the male cub, as he matures and strives to match his father's strength. Due to legal restrictions preventing the use of the name Kimba in the English dub, the production team reverted to the original Japanese names for all characters.