Gosh. Crumbs. Well, that was... um, the 1970s. (Mind you, I can't deny that Japan in general has a disturbing tendency to accept rape as entertainment.)
Hanzo the Razor (played by Shintaro Katsu, also of Zatoichi and Lone Wolf and Cub) is a cop. However this the Edo era, so "police investigation" generally meant "find someone and torture them until they confess". Hanzo usually fights with knuckledusters, a manriki-kusari (chain whip) and other weapons that really were used by police officers back then. (This is pretty brutal and the film has fun with blood spurting.) Surprisingly I don't think I ever saw him using a razor, but that's a good thing since any such scene would have been terrifying.
I'd describe Hanzo as the ultimate 1970s anti-hero cop. (This film is gloriously 1970s. The music alone will tell you within ten seconds that it's the spirit of Isaac Hayes who took us to the 19th century, but look out also for the magistrate in tinted glasses.) He's the film's, um, hero, but he does things like:
(a) refusing to swear his policeman's oath about not abusing his authority or taking bribes. On being challenged on this, he responds with a rant about how the system itself is dirty. Dodgy organisations and groups give "donations" to the police, then can't be investigated because they say they're outside the cops' jurisdiction. This scene is kind of terrifying, because Hanzo's refusing to be subordinate and face-saving to a room full of stupid, macho thugs who'd cut off your head in the street because you hadn't bowed low enough.
(b) forcing his servants to torture him, which is pretty disgusting. They're crushing his legs with stone blocks. Even Hanzo's own chief freaks out on seeing it. "We ourselves should know the pains of the criminals we torture."
(c) refusing to obey direct orders, calling his corrupt chief a snake to his face.
(d) expressing gratitude by breaking your nose so violently that everyone believes you're dead. (It's a practical solution to the immediate problem, but yeeesh.)
He's a man of bone-breaking honour who never compromises. You respect him, sort of, but you'd run a mile if he walked in the room.
On top of all that, though, is the rape thing. It's Movie Fantasy Rape, in which the victim will always end up saying "no, don't stop". It's as realistic as dragons and flying unicorns. Also, in fairness, the rape/sex scenes themselves aren't wank material. (There will be nudity later, yes, but not when Hanzo's "interrogating" his suspects.) Sometimes they're just deranged, like the one where a woman's half-stripped, bundled up in a net and then repeatedly hoisted and dropped on to Hanzo as he lies face-up underneath.
There's also a scene where Hanzo hits his penis repeatedly with a stick, then has sex with a bag of rice. Just... what?
This is lurid nonsense. I couldn't argue with anyone who was offended. However, shockingly, the movie as a whole is pretty cool. Hanzo's such a monster that you can't wait to see him let loose on the baddies. (These can be satisfyingly vile, incidentally, with the film putting a size twenty boot into the idea of the noble samurai. Mr "Jump in the River" is an absolute bastard.) Not everyone (to put it mildly) will be able to stomach the rapes, but they're always consensual in the end and no different in plot role from the Bond girls in a 007 film.
The film's ending is odd. Hanzo identifies the aristocrats who'd been behind everything... and then leaves them alone. The only people he kills are enemy swordsmen who'd tried to assassinate him. This is weird. Instead of having the final act you'd expect, we jump into a completely different mini-story that has nothing to do with the rest of the film. Two children are trying to kill their terminally ill father! He's terminally ill and in constant pain, with only a month to live! Hanzo disapproves, though, because patricide has a mandatory sentence of crucifixion. What can our compassionate Friend Of All Children do to help? (Hint: it involves a heartwarming noose.)
There are three films in this series and obviously I'll be watching them all. This movie is freaky. Shintaro Katsu is an improbable action hero, being ugly and tubby, but that's part of what makes him memorable. I've seen people trying to defend this film as parody... uh, no. I don't buy it. Don't play that card in an attempt to justify the fact that you enjoyed this film. I wouldn't even call it exploitation. (If it were, you'd expect it to be more, well, exploitative. Mind you, some definitions of "exploitation" include John Carpenter's Halloween, spaghetti westerns and the entire chambara genre, so what do I know?) Maybe the later films in this series get parodic, but for me this is just pure mainlined 1970s and trying to nail your eyelids to your skull. You couldn't make this film today, but it exists.