While filming, Tatsuya Nakadai was afraid during most of the sword and spear fighting scenes because real swords were being used, a practice now forbidden in Japanese films. His concern was not alleviated even though professional swordsmen were employed during the choreographed swordplay.
This film is an example of how Masaki Kobayashi opposed the idealisation of Japan's feudal system. The film repeatedly challenges the honour system of the samurai. Challenging such notions was part of a post-occupation movement in Japan.
Seppuku and harakiri (the U.S. working title) both mean to commit ritual suicide in Japanese. However, seppuku is the formal term, derived from the kanji characters for "hara" (belly) and "kiri" (cut); harakiri is the cruder, less polite term for this act.
Stage-trained actor Tatsuya Nakadai and older film actor Rentarô Mikuni could not agree on an acceptable speaking voice while sharing the film stage. Nakadai spoke loudly and Mikuni spoke softly, with each citing their related acting experiences for their choice. They strongly disagreed with each other. The director, Masaki Kobayashi, halted filming and stated that he would not resume until both actors came to an agreement. They did, after stopping the shooting for three days.