Yami's sword is called "Black Asta" or "Demon-Slayer Sword." In the anime and manga series "Black Clover," Yami Sukehiro is a character who wields a unique katana known as Black Asta. It is a powerful weapon with a black blade and anti-magic properties.

Black Asta's design and abilities are distinct from traditional katanas in the series. It is infused with anti-magic, allowing Yami to counter and nullify other magical attacks. As Yami's primary weapon, Black Asta aids him in his role as the captain of the Black Bull squad and in battling powerful adversaries throughout the series.