@Anomander The only right answer.
@NamelessGent @Epsilon04 Really anything by this author is dark. All of their works have a lot of surreal elements, and delve into depression. They have a 1 shot called "Flan Wants to Die" for example. This author has a cute style, and makes cute moments, but make no mistake their works are dark and usually bring up suicide. For me I think their works are relatable, since depression often feels like a listless surreal dream.
Also this series has always had various dark themes/humor, for example they have a literal hole digging club that's run by an alcoholic teacher, that can't stop digging holes. That's a text book example of gallows humor.