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 as part of the Complete Works with Adventure Ruby (冒険ルビ, Bouken Ruby).

Volume 1 includes "Kindergarten" and "First grade elementary school" serialized from 1965.
Volume 2 contains the serializations in "second grade", "third grade" and "fourth grade". This entry is currently only for the Third grade chapters.