Complex sentence: Inevitably, the assassins fall one by one while they inflict devastating casualties on the guards, eventually killing all of them, until, at last, there is a one-to-one sword fight between Shinzaemon and Hanbei, with Naritsugu watching.
Split into simpler sentences: Inevitably, the assassins fall one by one while they inflict devastating casualties on the guards. Until, at last, there is a one-to-one sword fight between Shinzaemon and Hanbei, with Naritsugu watching.