While Kill! is based on the same novel that Kurosawa used as the source material for the Yojimbo sequel Sanjuro, the movie of which I was most reminded was Sword of the Beast. The plots of both films revolve around samurai who kill a higher-up as a result of prodding by another samurai, only to be betrayed by that samurai when the deed is done. Both films are, not coincidentally, included in Criterion's Rebel Samurai boxset (which has no spine number).
The difference, of course, is that the earlier film is deeply serious, while Kill! is very much a comedy. The film focuses on two men, one a samurai who gave us his position after becoming disenchanted with the life, the other a lowly farmer attempting to work his way up to the very same perch. They meet briefly, before soon finding themselves on opposite sides of an internal clan battle. Like the confusing Samurai Spy, there are plenty of double crosses and switched allegiances in the film to keep the viewer busy. But unlike that film, these elements are so clearly presented as absurd that they end up being played for laughs. There are brief moments when the material can be too slapstick (including one of the weirder implied sex scenes I've ever seen) but overall Kill! has a dryness to its winking that allows the film to have its cake and eat it, too, like Scream minus the 90s meta edge. It makes for a very entertaining film that can be enjoyed on several levels.
I enjoyed Samurai Rebellion, Sword of the Beast, and Kill! so much that it seems especially disappointing that Samurai Spy - the only other film in the set - failed to move me. But as I slice my way through the Collection and its vast samurai presence, it's becoming increasingly clear that the subgenre has a broad range of styles, tones, and thematic underpinnings to offer.