The film alternates between two timelines: the present (the revenge event) and the past (leading to the event). More or less like Harakiri (1962) which is also written by Shinobu Hashimoto.
The editing and going back and forth between the present and past plays a big role in comprehending the terrible situation the protagonist is being put through by the system. I'd imagine if the movie played in a linear fashion and presented the revenge event timeline only, the viewers…