Sword of Satan improves on the last entry with lots of action and a story with more surprises than usual. The film opens with an atmospheric scene which hooks the viewer.

Leaving a tavern one dark foggy night, Kyoshiro Nemuri is approached by a woman in a noh mask who begs him to purchase her for the night. Nemuri at first accepts, but when he gets her home, the woman's mask and cultured background annoys Nemuri. He insults her and leaves. When, the woman kills herself, Nemuri feels a rare bout of guilt. The woman had a boy charge, the illegitimate son of a clan leader. The clan originally tried to kill the boy to protect the heir apparent, but now that both of the other heirs have died, the clan must have the boy or be dissolved. The cynicism of the action disgusts the usually cynical Nemuri, who vows to do only what is the best for the boy. In addition there is a female assassin who wants Nemuri dead for killing her brother (in the third film).

Along the way in achieving happiness for the boy, Nemuri kills about three dozen people, breaks up an illegal abortion racket, and interrupts a black mass. Director Kimiyoshi Yasuda, who directed the third entry in the series Full Circle Killing, stages the action with a sure hand. The battle at the black mass re-uses the P.O.V. action style that Yasuda had used in the fight on the steps in the third film, yet the effect plays better here. In addition, the action is more plentiful and violent than in the last entry, with a rousing finale at a temple. Finally, this entry brings back the trippy effect of Nemuri's sword seeming to leave a trail of light when he does the Full Moon Cut, which was missing from the last entry.

Sword of Satan is an all around appealing and exciting entry in the Sleepy Eyes of Death series. It is not the best one thus far (that is easily the fourth entry),but solid chanbara entertainment.