Demon Weapons (魔武器, Mabuki), often called simply Weapons for short, are human beings who have the ability to transform into a weapon. At the DWMA, they are paired up with Meisters, humans who are able to wield them in their Weapon forms. Together, they can achieve a greater amount of power than they would on their own.
The first demon weapons were created 800 years ago prior to the start of the series. Both Eibon and Death sought a way to even out the odds between the strife of witches and humans. Inspired by Excalibur, Eibon sought to create the demon weapons. Both him and Death agreed to do so required the use of a witch soul.However, both found the experiment inhumane and covered up it's instructions. Having taken a peek of the instruction with the use her tracking spiders, Arachne following instructions found within the Book of Eibon. To create a Demon Weapon she murdered a witch to use as a sacrifice and join a human soul and a object . Using the witch, which has transformative properties, Arachne joined an inanimate weapon and a human soul together to create a Demon Weapon, in which had the ability to transform from human to weapon form. 
This act branded her the most brazen heretic witch in the Witch Order and caused her to be hunted from her own kind and Death himself. She destroyed most of Lost Island after setting it to explode and evaded from her pursuers. However, she was cornered in Loew Village by Death and was thought dead
Demon Swords and Kishins
Despite their unwanted appearance, Demon Weapons were soon accepted into the world. The Eight Warlords were one of the groups to adopt demon weapons into their rank such as the likes of Vajra. However, their existence also made the possibility of a Kishin come to be. During a great battle, a meister was so terrified of death he began secretly feeding his weapon pure human souls with the hope of attaining more powerful for himself. He inadvertently created a Demon Sword and, eventually, a Kishin.
Grim Times Aftermath
After the foundation of Death Weapon Meister Academy and the end of the Grim Times, demon weapons over the years suffered discrimination from the likes of ordinary humans. Many incidents relating to their inexperienced and inadequante use of their power as known. The DWMA would do it's best to take in those weapons and train them to control their power. The use of the demon weapons even out the odds between the D.W.M.A and that of the Witch Order. However, their usage further their hatred, as a witch soul was used to create a Death Scythe and their own power was being used against them.
Humans with active Demon Weapon genes typically have the appearance of normal humans, though sometimes they do not. Their type of weapon and the weapon's appearance seems to depend on various criteria. For example, it could depend on a person's personality, or in the case of very old weapons, what time period they were born in. Weapon types are very diverse, with typical weapon types such as swords, shurikens, guns etc. along with more obscure ones such as mirrors, lanterns, and even 'pots.' When addressing Demon Weapons, the Japanese word for 'demon,' 'magic,' or 'demonic' is put before their Weapon forms. For example, Soul is known as a Demon Scythe. The way a demon weapon consumes the souls vary individually, with some weapons such as Soul and Ragnarok literally eating the souls, chewing and swallowing, while other weapons absorb through more unique ways such as Liz and Patty absorbing the souls to their magazines when transformed, and Nigus sucking the souls to her scabbard before being sheathed.
The blood of a Weapon is passed down, however, depending on the circumstances of an individual's life that blood may or may not actually be awakened. There are families like the Nakatsukasa clan which are made up entirely of Weapons and families like the Evans family where the Weapon Soul is apparently the only member to have inherited the Weapon blood for numerous generations. When becoming a weapon, clothing and everything on their person is carried on into the transformation. After becoming a weapon, the person is seen in their human form as some sort of reflection on the weapon while a completely black space is viewed inside the weapon. Inside their weapon, Demon Weapons seem to be able to have easy access to their souls, as Soul Eater can enter the Black Room in his mind from his Weapon form. They are still able to verbally communicate in their Weapon forms.
Often, in this dark space they are seen without their clothing on, save for a few details. In other cases they can be seen with all of their clothing. If two Weapons are resonating together and/or close together i.e. they are both used by one Meister, they can share this dark space. The Weapons also glow in the color of their souls when inside Weapon form. For example, Soul Eater has a blue soul, and as such, he is glowing a light blue in the dark space. Tsubaki has a yellow soul, therefore she glows yellow. The Thompson sisters have pink souls, so they glow pink. This glow is also present when the Weapons are transforming. The transformation usually involves the Demon Weapon being engulfed in a bright light and changing into the shape of their weapon before the light disappears. Elemental Demon Weapons display their elements when transforming e.g. Harvar turns into lightning when transforming into his Weapon form. The same also goes for Weapons with various "themes". Nygus is often associated with bandages, so her body dissolves into bandage-like strips when she is transforming.
Transforming into Weapon forms can be quite hard for rookie Demon Weapons. Some can only transform parts of their body, or cannot transform at all. The key to transforming, according to Sid, is to picture the weapon resting in one's soul. Mostly, it has to do with confidence and willpower.
These transformations also showed an useful side as Liz and Patty, two demon weapons were wielding each other during Kid's absence in the pyramid. They used tranforming as evasion, switching themselves between weapon and human in order to evade the mummies's attacks, showing that, somehow, demon weapons can also transform themselves straight to their intended wielder's hands.
Some Weapons in their Weapon form have certain components that move similarly to facial expressions; such as Soul, whose Weapon form has a red eye on top of the haft, which can convey his mood by narrowing when he is angry or ready to fight, or widening when he is startled. Ragnarok's Weapon form has a mouth on the blade near the guard. In Weapon form, Demon Weapons are usually invincible, and although they can feel the impact of the clashing with physical objects, they are protected by their Weapon form and cannot be hurt. Though they can also be hit by something extremely powerful and the Weapon can still be injured and may bleed, even in Weapon form.
At the DWMA, Demon Weapons are paired up with Meisters, skilled humans with great combat skills. With the Weapon's ability to strengthen their Meister, and vice versa, a Weapon and Meister team can combine their respective powers to become near unstoppable in battle. They can also make each other stronger by working together, making the bond between Weapon and Meister a strong and close one. In order to work together properly, the Meister must understand the Weapon's will, and vice versa. The Demon Weapon is not a normal weapon, or an inanimate object. It is a person with objectives. When perfectly in sync with each other, they can become a lethal force. Just by matching their breathing, a Weapon and Meister can fight flawlessly.
When paired with a Meister, a Weapon becomes extremely deadly. By performing resonance between a Meister and a Weapon, the Weapon can unleash a variety of abilities and can even change its physical form. This level of power can be achieved through what is known as a Soul Resonance, where both Meister and Weapon synchronize their souls with each other. In this state, their thoughts are both synchronized so well, that Weapons can even react to their Meister's emotions.
In theory, there is no restriction on who is capable of wielding a Weapon. Apart from meisters, it has been demonstrated that many other beings can wield a weapon: other Weapons within special cases such as a bond or being assisted by magic, animals, witches or even a soulless creature with a soul implanted within. However, in practice, the wielder's soul must be able to align with that of the Weapon or a rejection reaction effect will occur. This reaction is derived from a misalignment in the users' Soul Wavelengths, resulting from incompatible personalities, and appears to differ depending upon the individuals involved. For a Weapon and Meister to be compatible, they have to be able to accept and understand each others' personalities. Most compatible Weapon and Meister pairs seem to be opposites in personalities, especially seen with Black☆Star and Tsubaki, and Ox and Harvar. People with similar personalities like Soul and Black☆Star cannot become an efficient team. So far, Soul and Ragnarok are the only ones to show a rejection reaction though.
Symptoms of this rejection seem to vary on how much the Wavelengths are incompatible. When Black☆Star tries to wield Soul, their Wavelengths were so incompatible, that Black☆Star could not even lift Soul from the ground, and when Black☆Star sent his Wavelength through him, it caused the Demon Scythe physical harm. In the brief moment when Maka couldn't resonate with Soul, the rejection reaction was milder, but still harmful, as even though Maka is able to wield Soul, his Weapon form is extremely hot to the touch and she severely burns her hands until she can resonate with him again. Ragnarok's rejection reaction affects Crona as well as they both share the same body, and when their Wavelengths become misaligned, dozens of Bloody Needles erupt uncontrollably from Crona's body and the pair loses their ability to utilize th♙ Black Blood. A rejection reaction can be taken so far up to the point that a Weapon and Meister permanently lose their ability to synchronize their souls. At the DWMA, Weapons and Meisters can also change partners if they wish.
At the DWMA, the duty of the Weapon is to protect their Meister at all costs in battle. Seeing as how Weapons do not play as great a fighting role as their Meister, it is common for them to be in the shadow of their Meister; as noted by Ox while he is observing Patti sparring with the other students. They are often more renowned once they become Death Scythes. In a Meister and Weapon partnership, the Meister is also the dominant figure, as the Meister's decisions are often more considered instead of a Weapon's, and Weapons also have a duty to follow their Meister's commands. However, some Weapons break this duty, mostly because they view their Meister as not just a partner, but a close friend. In cases like this, in order to ensure their Meistersinger safety, they sometimes refuse to obey their Meister's commands and criticize their decisions.
Types of Demon Weapons
Most Demon Weapons are able to transform into Weapon forms, and transform a part of their body into their Weapon form when fighting on their own. However, they are not much of a threat. However, with a Meister, a Demon Weapon can unleash its full potential by combining their strengths with their Meister's. Some Demon Weapons have special characteristics, such as the Nakatsukasa Clan's multiple Weapon form transformation. Some Weapons can also have elemental properties, such as fire and lightning, and can generate these elements even on their own.
Autonomous weapons is a conjectural term given to demon weapons that are extremely skilled and are able to fight without restriction in spite of not being paired with a Meister. An autonomous weapon can be deadly without the general necessity of a meister even being present. 
While Demon Weapons are known to either be unskilled or have skills to a considerable degree, those who fall under this category are extremely competent and are unable to be traditionally wielded, even by the most of eccentric of meisters. However, it is more than likely that no matter the strength the Auotonomous Weapon may seem to have autonomously, they are not actually at their full potential as a Weapon. Examples seen in the series is Giriko, Justin Law, and even possibly Eternal Feather.
Dark weapons is an conjectural term given to demon weapons who've started the process of consuming human souls. Though not named in either the manga or anime, weapons who're noted to start consuming pure human souls have often been attribute in being closer to becoming that of a Demon Sword and eventually, a kishin.
Also, those who consumed human souls are often known to have the ability to consume the soul of their meister given a chance. If a dark weapon manages to over-hunt enough pure human souls, they'll become what's known as a Demon Sword. The exact number it takes to become a Demon Sword is unknown.
Main article: Death Scythe
Demon Weapons are known to have a 'true form.' As a human soul and a Witch Soul was needed to create the first Demon Weapons, if a Weapon consumes a certain amount of Evil human souls and a Witch Soul, they turn into a powerful Weapon known as a Death Scythe.
It is interesting to note that normal weapons can transform partially by replacing a body part with the blade while Death Scythes can burst weapon parts out of their body without replacing anything.
Main article: Demon Swords
A Demon Sword is the polar opposite of the Death Scythe, created only from over-hunting of pure human souls from a dark weapon. Individuals who are Demon Swords are only one step away from becoming a Kishin. Only Ragnarok and Vajra are known demon swords.
Demon Swords are known to be powerful demon weapons on par with that of Death Scythe and are also, like dark weapons, able to consume their meister's soul. In addition, their as durable as that of a deathscythe. In the case of Vajra, a demon sword is strong enough to damage even a shinigami.
In the anime, it is shown that in a rare case, a meister such as Maka Albarn, who's human and has a father who carries the demon weapon gene within him is capable of utilizing partial weapon transformations and sprout weapon, despite not being a Death Scythe.
In this state, Maka became incredibly skilled, able to content and fight on a level similar to that of Death and Asura and was even able to damage and hold her own against the Kishin for a time. A major drawback to this, however, is that the ability can only be utilize while an individual being unconscious and being awake disables the gene .
Demon Weapons in the series have a variety of abilities given due to their heritage. They're highly skilled in wavelength communication, which allows communication on a spirit level with meister and, most importantly in combat, allows them to receive or give energy. Demon Weapons also have the ability to partially transform their body parts in to a weapon. Depending on theme and abilities, Demon Weapons can also convert energy they are given into a set element such as fire, electricity or a slicing attack. The most reknown abilities for a Demon Weapon to have is the ability to eat/absorb the soul of a vanquished foe in order to make them stronger. They're noted as the true beings only able to become a kishin., Meisters like Asura having to resort to finding a method of combining himself with their weapon to gain the status of a kishin.
There's also a number of given traits a demon weapon may have such as the Multi-Form Ability, in which a weapon can transform into multiple weapons. The Nakatsukasa Clan are known to have this ability, having passed down their previous weapon forms to Tsubaki Nakatsukasa.
List of Demon Weapons in Soul Eater
- A common inconsistency in the anime is those who can eat Souls. The anime and manga both explain that only Demon Weapons can eat souls. In the anime, people such as Lupin, White☆Star, Al Capone, and Jack the Ripper contradict this. However, in the manga, there's no mention of any of these character consuming souls. All of their crimes are those like Thievery & Murder. No characters mentioned above have actually consumed souls within the Manga version of Soul Eater.
- Only Asura has been able to eat a soul and he's classified as a Meister. However, due to his eccentric abilities, he consumed Vajra & resonated to gain the ability to consume souls.
- ↑ Soul Eater Manga: Chapter 99
- ↑ Ohukbo tweeted this was the case. Despite the translation from google, we're sure that what he meant.
- ↑ 3.0 3.1 3.2 Soul Eater Manga:Chapter 25
- ↑ 4.0 4.1 4.2 Soul Eater Anime: Episode 27
- ↑ Soul Eater Anime:Episode 34
- ↑ Soul Eater Manga: Chapter 6
- ↑ 7.0 7.1 Soul Eater Manga: Chapter 99
- ↑ Soul Eater Anime: Episode 27
- ↑ Soul Eater: Chapter 28
- ↑ Soul Eater Manga: Chapter 5
- ↑ Soul Eater Manga: Chapter 7
- ↑ Soul Eater Manga: Chapter 5
- ↑ 13.0 13.1 Soul Eater Anime:Episode 51