Jungle Emperor (Third Grader) summary:

As a manga tie-in for the then ongoing anime in 1966, this spin-off was serialized for a younger audience. As a little lion cub in the jungle, Leo must find a way to stop an aggressive red rhinoceros from hurting his jungle friends. Watch a boxing match between Leo and a rogue lion, Bubu.  Help Leo save a brave hero as he gets revenge on Lubar, an elderly leopard. Finally, learn about Laiya's brother and how a hydra-snake was able to devour their entire family. These chapters of the Shogakukan Sunday Comics were re-released in 1994 with the Complete Manga Works edition of Bouken Ruby (冒険ルビ).