Shusui

One Of the 21 O Wazamono or '21 Great Edges' of the world. It was the meitou of the Samurai Ryuuma, who appeared as an zombie on Thriller Bark that had been given Brook's shadow. Zoro took the sword from Ryuuma after he defeated him. It is designed to increase the damage potential of the user, but Zoro has commented that Shuusui's greatest attribute is its hardness; saying that even if a dinosaur were to step on it the blade wouldn't bend.

While it deals a heavy blow and is extremely hard, Shuusui has a few major problems of its own. Just as Sandai Kitetsu turned out to be a "problem child", Zoro describes Shuusui as having a "temper" making it harder to wield. In comparison to Yubashiri which was extremely light, Shuusui is extremely heavy which he discovered while fighting Oz. Its weight increases the power of Zoro's attack but decreases his control.