Considering how 90% of the series that are mentioned are romantic series, I decided to post some memorable ones which have almost or no romantic elements.

Bokurano - Basically Neon Genesis Evangelion (which is a tragedy in itself) on lots of depressants; this is one of the most depressing non-romantic series that I have read. Written & drawn by Mohiro Kitoh, who is a God at creating depressing / tragic series. Has a bittersweet (almost a downer) ending.

Narutaru - Made by the same creator as Bokurano, and has similar themes, except that it is more darker by nature, more violence, taboos, and uses 'dragons' (not quite what you'd be expecting) instead of a giant mecha. Has a downer ending.

Uzumaki - Dark and very disturbing atmosphere overall, you get lots of violence and horror with no hope of escaping; leads to a downer ending.

Berserk - Extremely violent series with strong (almost) hentai elements, but the motif is pretty tragic. Still on-going, but the protagonist is a doomed-antihero type, so most likely a downer ending.

i say Clannad has to be really sad

Spiral Suirni No Kizuna


HE RECEIVE TRAGIC FATE AND DESTINY


YET HE CAN STILL SMILE ADORABLY

Elfen Lied! and Kuroshitsuji

Flowers of evil and Koizora ... it was complicated and sad

I would be more suppressed to meet a person who didn't cry at some point reading Bitter Virgin parts of that where like a punch in the stomach to me so yeah Bitter Virgin would be my choice also.

ohhh and also Sand Chronicals

Elfen Lied

Koizora soooooo sad manga

Kimi No Iru Machi makes me scream at the screen. Every. Issue.

Ok maybe an exaggeration but its so frustrating still!

Oh Gawd yes.
This made me cry ;-;

Oooh!! Spiral is one of the SADDEST mangas I've ever read...!!

Uhh,..bitter virgin??~^^

tsubasa chronicles...is the only tragedy manga ive read aside from vampire knight, w/c is not finished yet(manga)

well... um... i guess kitchen princess....