Murasame

One-Cut Killer: Murasame is a Teigu in the form of a long katana that is used by Night Raid member Akame. Akame Ga Kill!: Zero reveals that it was formerly used by Gozuki, who personally trained Akame and several other children to become assassins for the Empire.

Abilities
Murasame is a cursed blade that can kill a person with only one cut. Once the sword pierces skin, a poisonous curse spreads into the victim, killing them within seconds. Akame states that cleaning this weapon is very dangerous because of this ability. However, this ability only works 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.

Trump Card
In the Manga, Lubbock mentions that Akame cannot use her trump card supposedly for unknown reasons. Later, Akame reveals to Tatsumi that in order to use Murasame's Trump Card, one must discard their humanity and embrace their inner demon. However, what the Trump Card actually does has yet to be revealed.

In the anime, its trump card is a speed and strength enhancer; by cutting oneself with the sword and resisting the poisonous curse, therefore accepting responsibility for all the lives taken with the weapon. The user's scleras turn black and black markings appear around their pupils. Red markings also appear along the user's body and remain as scars once its effect diminishes.

Trivia

 * Murasame literally means "village rain" and is often associated with a type of rain that falls hard, then gently, in fits and starts.

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Murasame Мурасаме 一斬必殺：村雨