In the manga and anime series "One Piece," Roronoa Zoro, one of the main characters, obtained the sword Shusui through a significant event known as the Thriller Bark arc. Here is a summary of how Zoro acquired Shusui:

During the Thriller Bark arc, the Straw Hat Pirates, including Zoro, encountered the pirate Gecko Moria and his crew on the haunted island of Thriller Bark. Zoro engaged in a fierce battle with Ryuma, a legendary samurai zombie controlled by Moria.

During their intense duel, Zoro's original sword, Yubashiri, was damaged beyond repair. However, Zoro managed to defeat Ryuma using his remaining two swords. Impressed by Zoro's skill and determination, Ryuma entrusted Zoro with his legendary sword, Shusui, as his final request.

After the battle, Zoro formally accepted Shusui as his new sword, incorporating it into his swordsmanship style. Shusui is a treasured blade from the country of Wano and is known for its immense strength and status.

It's important to note that the events described above are specific to the "One Piece" storyline and may be subject to further developments or interpretations in the series.