After the massive success of Jungle Emperor in Japan, Dr. Tezuka created a sequel series in 1966, locally titled The New Jungle Emperor or Onward, Leo!. Unlike the first series co-produced with NBC, this sequel was an independent production that closely followed Tezuka's original manga. As a result, it had a darker tone, with significant character deaths and sorrowful episodes. NBC deemed the content unsuitable for its viewers and refrained from airing it in the US until 1984, after they had already used up their initial 52-episode run. The show then broadcast as Leo The Lion.
Set years after the original Kimba series, the story features an adult Kimba, now with Kitty as his mate and two cubs. The plot mainly follows their son Rune as he matures and strives to match his father's strength. Due to legal issues preventing the use of the name Kimba in the English dub, the characters were given their original Japanese names instead.