Sabu to Ichi Torimonohikae is an old manga from the Sixties. It’s set in old Edo. The detectives are a young thieftaker named Sabu, and an old blind masseur/swordsman named Ichi. Naturally, the old masseur is very underestimated.
The mysteries seem to be a little less grotesque than some Japanese mysteries are. But it’s still pretty much concerned with lowlifes and bad behavior, including some from the detectives. There’s also a fair amount of samurai violence. It gets pretty grim, albeit not as grim as Lone Wolf and Cub.
It’s not available in the US, but there’s a scanlation here.