While Nichi Mei and Dakota Cha use knives and other weapons, their main swords are known as the annointed Tachi. Many modern characters using swords are depicted as using katanas or broadswords. Below is more information on the Tachi.
In my novel, death kissed each blade so that it could cut through demons. While the demons are not destroyed by the Tachi, they are sent back to their realm if the blows dealt are considered “fatal.” However, to deal a fatal blow to a demon requires incredible skill and accuracy as only certain areas of the demon “body” are vulnerable to attack. Typically the fight with the Tachi is to keep the demon at bay until a more permanent containment or “death” can be dealt to them.
One might ask why the swords used are Japanese? That is because it is the culture the main character comes from. He is an older Japanese man and so that is where the cultural items are pulled from.
As readers will learn, the liminal spaces adapt to the perceptions and expectations of the mortals that happen to encounter them.
Aren’t their more efficient weapons that could be used? Yes, however, these are ancient beings and the items they have are sacred pieces from across the ages.