What's the saddest anime you've watched?

I'm so into animes..which is why I opened this thread. 

I would really like to know what the saddest animes you've ever watched is...so if you're seeing this thread..you know what to do. hawhaw

Mine is grave of fireflies. 

Oh man! where do I begin from?

Grave of the Fireflies is one of the most beautifully rendered, amazingly paced, wonderfully written anime movies I've ever seen.

…and I will never, EVER rewatch it. Phenomenal movie, I never want to see it again.

That movie made me cry so hard I got physically sick. I still can't process parts of it. It's just so sad. 

It will make you curse humanity.

Your soul will feel empty. But I think it's an incredibly important movie and I think everyone should watch it. Atleast once in their lifetime.

Clannad: After Story

Clannad didn't hit me (since I didn't like the "omg so sad!!!"), but After Story properly left me in tears and feeling things.