I'd like to recommend King of Thorn! I'm not sure if it counts as disturbing? It's got some pretty gore-y moments but overall it ends on a really positive note! But yeah, there's a lot of scenes where people get straight up eaten by giant monsters, and one of the characters ends up plunging their bleeding arm into alcohol, crumbling into stone, and turning into a griffin.

Another great one is Bio-Meat! It's another survival horror. Basically, Japan has created this creature that multiplies at an astonishing rate and can eat anything in order to solve the food crisis. One of them gets out, and long story short well...Humans become some of their favorite food. There's a couple arcs in the story, and I really enjoy the whole thing :)