As someone in the US, I'm actually more use to seeing the title 'Grave of the Fireflies', I don't think I ever saw it referred to as Tomb of the Fireflies before now.

That said, I actually walked away hating this movie despite enjoying a lot of Ghibli films. For me there is a big problem that the characters honestly have very little personality to them, they are basically just archetypes with no depth. The movie doesn't make you sad because you care about the characters, it makes you sad because you are watching children die. If you remove that one aspect, there is absolutely nothing else of interest here. It's something I think is a lazy writing trick because there is virtually no one who isn't going to be sad watching children suffer regardless of context.

The worst part for me is at the end when you see all the faded images of the little girl doing all these cutesy poses in the army helmet, something that is just there to go 'See how cute she is? And she is dead now!' despite all those things she did there having nothing to do with anything that actually happened in the movie, it's just trying to make you feel bad at that point without really saying anything.