One Piece Chapter 51, page 15: Roronoa Zoro Falls Into the Sea

Zoro stands tall, raising his swords as he pants, "Roronoa Zoro." Mihawk smiles with respect and reaches for the massive hilt on his back. He declares, "I shall remember it, and to pay my respect to you as a fellow swordsman, I shall end this duel with my Black Sword, the world's strongest sword. For your strength is not often seen in this world." A translator's note at the top of the panel explains: "tl note: black sword is kokutou in japanese."