So far, it's Berserk and I'm not even done. Messed up back-stories. One Piece has quite a handful of sad moments but there's a lot of happy moments to balance it out. Berserk on the other hand... >.> depressing af but enjoyable.
kami nomi zo shiru sekai. Now the whole manga was awesome..but that ending..That ending was just too sad. It had me questioning my humanity. If the sadness from watching school days is a 100/100, the manga ending of kami nomi zo shiru sekai is a 75 imo