Haré + Guu, vol. 1 (Amazon.com)
I just watched the first disc, & I really enjoy this series. Haré (Har-aye) is a 10 year-old boy living on a tropical island, & doing fine until Guu, apparently a little girl is adopted by his mom. Guu is a shadow creature that can devour elephants and whales without gaining an once, or even harming those she 'eats.' She even swallows an entire class of students, who while having a siesta, all had the same very weird dream. But it was no dream, they were all inside Guu. So, poor Haré, upon returning from the boy's restroom, notices that nobody is there, except Guu, who just then burps.
He panics, & goes to tell the Principal, but when they return, everybody is there, all having awakened from sleep, and having been discussing their common 'dream.' 
So here is poor Haré, trying to figure out exactly what happened to all the animals he was trying to show Guu, & finally realizing that Guu ate them. He then also realizes that she is the very scary shadow creature that was chasing him a while ago. But he cannot convince anyone that she is anything but a harmless little girl.
