Gamba no Bouken

Both animes tell of animals generally considered adorable, fighting for life and death with a true samurai spirit, against a threatening big enemy! They're also not suitable for young children (although Gamba isn't as violent as GNG, but rather bloody and dark nonetheless). I recommend both if you are a fan of dark animal animations and animes! You will not be disappointed. 

Both series are from the same era (Genshi Shonen Ryu from 1971 and Gamba no Bouken from 1975) and have a quite similar plot: A young hero fight against a big threatening enemy. They are very dark and bloody at times.  

Both are survival series in which the main cast is being preyed upon by foes much larger than themselves. Bloodshed and violence serve to increase their intensity and you never know who's safe. 

Curiosity sometimes can give someone encourage to commit such dangerous adventure to satisfy his curiosity. "What outside world like?" "What kind creature or peoples we can see out there?" That what Kuu and Gamba thinking before starting his journey to find new world they both never seen before. A simple story which can be enjoyed by everyone.