Lesser known western animated feature. Like Watership Down in it's bleakness... Except with dogs (written by the author of Watership as well). I first saw it when I was 7-ish or so - my old man picked it up at the library, thinking it'd be a kid's cartoon. I turned out crying my eyes out instead. I recommend it for all kids! Not enough of them understand death and cruelty well enough.
Also, it's still quite capable of making adults cry. Powerful film.
Hmm, that's a tough one actually. A little of both, I guess.. Probably closer to Grave of the Fireflies. Think Bambi meets Grave meets.... Thelma and Louise (lol).
Anyhow, even if you find yourself not too depressed by it, you'll probably find yourself entertained anyways. Good enough.
[edit] It's a hard film to get ahold of, I think, but someone was kind enough to put the uncut version Youtube. It's in multiple parts, if you're interested.