Dark Knight's Sword is one of the magic swords described in Monster Girl Encyclopedia World Guide - Side II.
Guide Book Entry
The knights of Lescatie have officially adopted mamono realm swords, which are made from "Mamono Realm Ore", such as "Mamono Realm Silver" and "Mamono Realm Iron". Mamono Realm Silver, mined in the Mamono Realms, has the property of easily harboring mamono's magic. By processing it, you can create a weapon that does not kill, but when an opponent is wounded by it, it damages his mana rather than his body, thereby taking away his strength to fight and not harming his body. Perhaps because mamono realm ore has a pink sheen, mamono realm metal also has a similar sheen, and in some cases the entire sword can emit a pink or pale purple glow. However, at first glance, mamono realm swords are no different in appearance from ordinary swords, and a person would not be able to tell them apart unless he or she has a bright talent for sensing magic. However, mamono realm ore mined in Lescatie has a richer shade of pink or purple, and the sharpened blade will have a mysterious luster like a gemstone. Like the dark knights of Lescatie who use such weapons, mamono realm silver blades will have a beautiful and enchanting appearance.
Among the monsters I encountered on my journey to Lescatie, of those who used weapons like the Lizardmen, every single one of them carried mamono realm weapons. This seems to have something to do with the fact that not only do these weapons use ore mined in the mamono realms, but the monsters hate hurting people as much as they hate killing them. Swords made of mamono realm ore are rarely seen as weapons used by humans, mostly due to the fact that blacksmiths in the human realms almost never get their hands on this ore. But on the other hand, such weapons are not only common monster weapons among the dark knights of Lescatie, but are also widely used as official equipment of the Mamono Lord's Army.
Since the mamono realm's weapon is light enough that its weight is barely felt compared to a normal sword, and it is impossible, due to its characteristics, to harm a human even by accident, it appears to be an excellent weapon for mamono. Although, because of its ability to harbor mamono mana, if such a weapon were to end up in the hands of a human, the mamono mana from the blade would probably affect him... is that probably another reason? A polished mamono realm sword, full of a beautiful and mysterious glow, is so enchanting to those looking at it. In the lands of men, it is often enough to recognize it as a "cursed object." Among other blades, however, the magic found in Lescatian swords is more aggressive. It is said that a woman who takes such a sword will be corrupted and will be transformed into a beautiful monster, suited to the sword's charms.
In fact, people, especially women, are often transformed by these swords into mamono. Furthermore, when a human man picks up such a sword, which belongs to the dark knight, he will unwittingly be enveloped by the magic of the wielder that is in the blade and have his heart bewitched. In the end, he, along with the sword, will serve the dark knight, though as her husband... This seems to be the reason why, when I, as a dark knight rookie, was assigned to carry weapons, I saw many swords in the armory that were simply laid out in rows. This is probably also a trap to counteract intruders. At first glance, a beautifully gleaming sword made of mamono realm ore looks like a precious weapon. And if a person's gaze was attracted by the glitter of this sword and he tried to draw it, it would not be hard to imagine his future, which would involve the dark knight.[1]