Yeah, Samurai Rebellion is an amazing movie. I'll confess to not having seen Fuefuki but I want to. If you haven't seen Hara Kiri, do - same director as Samurai Rebellion and absolutely riveting performance by Tatsuya Nakadai (with an excellent score by Toru Takemitsu and a great script from the guy who wrote the first draft of Rashomon).
Another film that comes to mind is Samurai Assassin; really of the New Wave directors Mahashiro Shinoda's unrelentingly grim films most remind me of Shigurui but Kobayashi's two bitter samurai pictures have more in common with Shigurui's plot.
On a Shinoda note I could watch Double Suicide over and over again and also I do that is an amazingly bleak but absolutely memorable film.
Okay I'm off topic but perhaps worth noting that one reason I like Shigurui is it's like an incredibly disturbing and cartoony (haha, I am a wit!) version of these films.