Need the Saddest Anime possible

I am on a roll of watching the saddest animes that I can find.

In the last while I have watched:

-Steins Gate
-Ano Hi Mita Hana
-Tokyo Ravens
-Boku Dake ga INai Machi
-Hanbun no Tsuki ga Noboru Sora
-Charlotte
-Shigatsu wa Kimi no Uso (I almost cried on this one. I totally had to hold back)
-Toradora
-RE- Zero Kara Hajimeru Isekai Seikatsu
(So yeah, mostly more on the sad side of animes)

-Going to be watching:
-Plastic Memories

I've already watched some sad animes in the past. I just feel like I'm running out of them. I really am looking for something that will leave me more sad than I was at the end of Shigatsu wa Kimi no Uso...but so far to no avail. I need some help finding one.

Thanks in Advance!

Always thought Grave of the Fireflies won this award since forever.

Kimi ga nozomu eien

Hakouki shinsengumi!

Usagi drop
Clannad after story
Nana

Goldenboy

Deleon said it earlier, it 's this one:

火垂るの墓 / Hotaru no haka
Grave Of The Fireflies / Le tombeau des lucioles.

Elfin lied

A perfectly disturbing combination of sadness and gore

I guess it depends what makes you sad; I've felt bittersweet sadness from watching Serial Experiment Lain <3

Kuzu no Honkai