There's a story being serialized in comic unreal right now by the artist タケ called 寄生樹(parasite tree) that is probably one of the darkest publicly serialized manga I've seen in a while. While there isn't any overt guro(at least not so far up until the 3rd chapter) the themes are incredibly dark and practically snuff.

The story basically revolves around a group of traders that gather a valued aphrodisiac from a plant that blooms once a year only by corrupting and consuming the body of a virgin. Since the tree only reacts to a small percentage of young girls, they have to overcompensate by bringing many dozens to get any yield. Since they have to wait 30 days for the trees to blossom they spend that time raping and killing off all the remaining girls who didn't react with the plant.

This cat girl was selected as part of their yearly tradition where they select a girl who they pretend has impressed them/is special and they treat her like a queen basically and no one is allowed to touch her. Once the first buds sprout they then hold a feast where the main event is them brutally gang raping the girl. Since the cat girl was mean towards all the other girls they think it would be fun to give her to the other girls after raping her and let them do what they want with her. The next panel shows her corpse being dragged off implying she was killed by the other girls. More and more girls get dragged off as they are raped and killed over the course of the following days.

Again there's no overtly graphic guro but the story is honestly a lot darker and more chilling than 90% of the actual guro manga out there and I can't wait for the final chapter. It will probably be some kind of redemption ending but I hope it stays dark until the end where the traders "win".

On another note, I've noticed Comic Unreal has gotten a lot darker in general over the last couple of years or so. They always had Date but more and more recently there are artists making stories with death and hard corruption.