I have watched the entire video of Nekojirou-sou (a.k.a Cat Soup) anime, but I still don't understand the ending of Cat Soup, neither the plot. It started from 2 siblings cat, well I don't know how to describe the entire story, but at the end of the story, why is everyone "gone"?
I guess, the plot itself is explained fairly easily:
A cat named Nyatto embarks upon a journey to save his sister's soul, which was ripped in two when Nyatto tried to save her from Death. She trails after him, brain-dead. They encounter many brilliant, mind-bending situations, beginning with a disturbing magic show.
Taken from AnimeNewsNetwork
But the movie contains a lot of surrealistic parts and has many underlying themes, which makes it difficult to completely understand it. Many people see it more as a kind of art than just an anime movie. So, the interpretation of certain parts differs greatly from person to person. As far as I know, there is no official explanation about it, which makes sense, since it would take away a lot from the fascination, which the movie can provoke inside the viewer.
Psychology student here,
I saw the whole thing as a series of artfully programmed psychological attacks towards the audience, yanking at the limits of what most of us think is ok or not ok, is sad or happy. In other words, this short film is a deliberately designed emotional rollercoaster dressed up as visual art. I notice studio 4c always produce their anime with this in mind.
e. g. - the opening scene of short peace, another one of their productions, have colorful images explode out of the crouch of a loli girl, which is also blowing up her dress n lifting her into the air. Is that sexual? Not sexual? Is that ok?loli? Its just an opening scene, but i was on the edge of my seat. Sex is often used to yank at your strings in their movies.
If i had to apply a descriptive meaning to it, it would be something like "the things that happen in life that u try to do everything u can to improve/fix but nothing works, so you give up and everything suddenly turns better, altho it might all be just a dream/your imagination. Go ahead and try to understand the bs of life itself, good luck"
Its a very eastern theme, shinigami escorting newly diseased to the afterlife is a very common believe.