Murasame

One-Cut Killer: Murasame was a long katana-type Teigu used by Night Raid's Akame. Akame ga Kill! Zero reveals that it was formerly used by Gozuki, who personally trained Akame. During her battle with Gozuki, Akame steals the Teigu after fatally wounding him and she ends up replacing her Shingu Kiriichimonji (which is destroyed during that battle) with it. It was later destroyed by Esdeath during her final battle with Akame. It is said that the roots of Murasame lay in Wakoku, where the events of Hinowa ga Yuku! transpire.

Abilities
Murasame was a cursed blade that could kill a person with a single cut. Once the sword pierces the skin, a poisonous curse spread through the victim's body, killing them within seconds by stopping their heart. The curse appeared as black markings that originated from the wound and spread across the victim's skin. These markings vanished once the person had died. In the anime, the markings remained permanently on the victim's heart. Akame stated that cleaning Murasame was very dangerous because of its ability, which is why she used gloves when wielding the blade. However, this ability only worked on living, organic beings that have a heart, rendering it ineffective against Armor and Biological-type Teigu as well as machines and Yatsufusa's corpse dolls. Esdeath showed that it is possible to survive the curse by cutting off the affected body part before it can spread to the rest of the body. However, this must be done quickly, as Esdeath even stopped time to amputate her arm. The curse's black markings remain visible on the amputated body part.

A flaw of the blade being if there are two or more souls inhabiting one body, only one soul can be killed at a time. Akame used this to her advantage to slay the Tyrant, liberating Tatsumi.

Trump Card
Murasame's trump card was a performance enhancer titled Little War Horn that strengthened its user with the power of its poisonous curse. When the trump card activated, the user's scleras turned black with black markings appearing around their pupils and a dark aura enveloped their body. Red markings also appeared all over the user's body and remain as scars once its effect ended. These scars continuously cause the user to feel pain all over their body, even after Murasame is destroyed. The trump card placed considerable strain on the user's body and only lasted for a short amount of time. Akame only used Murasame's trump card during her final battle with Esdeath after she freed Tatsumi from Tyrant with Murasame.

In the manga, Lubbock mentioned that Akame cannot use her trump card, supposedly for unknown reasons. Later, Akame revealed to Tatsumi that in order to use Murasame's trump card, one must discard their humanity and embrace their inner demon. During his final moments, Gozuki also tells Akame the same thing in order to activate the trump card.

In the anime, the trump card is activated by cutting oneself with the sword and resisting the poisonous curse, therefore accepting responsibility for all the lives taken with the weapon.

The trump card remains permanently and makes the user's body feel heavy after getting used to it. This is shown when Akame cannot pursue Yomihime for two reasons, her body is heavy and her weapons were broken. The side effect, however, can be suppressed temporarily through herbal medicine that the Elder can provide.

Trivia

 * Murasame literally means "village rain" and is often associated with a type of rain that falls hard, then gently, in fits and starts. In Japanese poetic tradition, it is particularly associated with the cold rains of autumn.
 * Merraid finds the weapon "exquisite" when she first saw it in Gozuki's hands, implying she might be capable of using Murasame.
 * "Murasame" is also a name of a region on the carotid artery, where a group of vital points is located.
 * In the manga, the markings that appear on the victim's heart when the curse activates are sometimes absent, but they are shown when Akame killed Enshin.
 * According to Rongo Rongo, Murasame's roots lay in an island nation called Jinwa that is situated in the lands of the East.
 * In order to be able to use and bond with Murasame, the potential candidate would need to naturally see the blade as "beautiful" or "exquisite" as seen when Akame first got a closer look at the blade,while the average person or incompatible candidate will instead feel an ominous aura surrounding the blade and consider the blade "creepy",as seen when Ibara of the Four Rakshasa Demons who despite being powerful was not capable of bonding with the blade.
 * Wakoku, the eastern lands where Murasame originated, is the modern reading for the name given to Japan in ancient China.

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Murasame Мурасаме 一斬必殺：村雨