These are Not as dark compared to Claymore but are good options.
Aside from what others already suggested, I would also recommend:
Arifureta - From commonplace to world's strongest.
There is an anime adaptation to this, but it skipped a lot of content. (Ongoing.)
As the title implies, the protagonist started as the weakest.
Overlord
Has an anime adaptation. (Ongoing.)
The story follows an undead-lich that wants to take over the world.
Re: Zero - Starting Life in Another World.
Has an anime adaptation, with an ongoing remaster before continuing the story.
The story follows an average person, gets reincarnated to a fantasy world, where he can come back to life if he dies, and reverse time with all his memories before dying. Including the pain of dying.