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.
The ronin in the film say they had been in the service of Masanori Fukushima until he was exiled and all his samurai became masterless. The exile happened because Masanori had made repairs to Hiroshima Castle without permission, which was prohibited by law. Masanori and his son were removed from their domain and given land worth much less in Shinano Province (Nagano Prefecture).