The swords of Roronoa Zoro from One Piece are not simply weapons but integral parts of his character and style of fighting. He has had a few named katanas throughout the series, all with their own history. As a master of the Three Sword Style, it is a given to find Zoro with three swords at one instance, holding one in each hand and one in his mouth.
Wado Ichimonji is one of the most iconic and longest-held swords by Zoro. This white-hilted katana is very special to Zoro personally because it was given to him by his childhood friend Kuina's father, Koushirou Shimotsuki, after Kuina's death. That means the Wado Ichimonji symbolizes Zoro's promise to become the world's greatest swordsman due to his vow to Kuina. This is the sword consistently used in Zoro's most powerful techniques and often the one he chooses when using his One Sword Style techniques.
Another influential sword in his arsenal would be the Sandai Kitetsu, a cursed blade bought by Zoro in Loguetown. While it is of extremely high quality, its legend says it brings misfortune upon the person wielding it. In choosing to take up the cursed sword, Zoro showed confidence in himself and took up the challenge from fate.
The third sword that completed Zoro's set for much of the series was the Yubashiri, which he had been gifted in Loguetown. By the end of the Enies Lobby arc, this sword had been destroyed, further showing the dangers involved in Zoro's battles and thus his swords' durability.
After the destruction of Yubashiri, Zoro acquired Shusui, a legendary black blade previously handled by samurai Ryuma. Such an important sword that it was included in the 21 Great Grade Swords category, which showed further growth in Zoro's status as a swordsman. Shusui contributed majorly to many of Zoro's battles, helping to strengthen his reputation as a great swordsman.
Most recently, Zoro has acquired the Enma sword, which serves as a replacement for Shusui in his arsenal. Enma is an extremely powerful and historically famous sword, used a generation before by none other than Kozuki Oden himself. This makes it one of the rare swords that are able to bring out the Haki in its user; thus, it is a strong but not the easiest sword to control.
Several characters' sword names and features, indeed, hold more meaning with respect to Zoro's travel and personal growth as a swordsman. A good number of fans and analysts identify some of the links with the names of Zoro's swords and important events or themes in his lifetime. For instance, the obtaining of Sandai Kitetsu often means a phase of destruction and rebuilding in Zoro's journey, in particular with regard to his encounter with Mihawk.
In the world of One Piece, there is a ranking system for swords that includes an assessment of the quality and historical value of the weapon. Much of Zoro's growth as a swordsman was marked by obtaining a higher grade of swords. This grading system basically means that every time Zoro upgrades his blades, he's getting a power-up, increasing further his combat potential.
Zoro does not simply use his swords to fight. He has different styles depending on the number of swords used. Though most famous for his Three Sword Style, Zoro is also very skilled in both Two Sword Style and One Sword Style techniques. This thus makes it easy to adapt to different situations of combat and opponents.
On the other hand, the treatment and care of his swords also form an important part of Zoro's personality. He is seen cleaning his swords and taking good care of them all the time, showing the honesty with which he treats these weapons. He keeps them in a good condition not just for their effectiveness in battle but more for workmanship and history invested in each blade.
Zoro's swords show crucial development with respect to his character and his combat potential as he seeks to become a great swordsman in the world. Every new sword he acquires or masters is an advancement toward the quest and thus brings him closer to his ultimate goal. Many of the legendary swords also reflect on Zoro himself, foreshadowing his potential to become legendary within the boundaries of swordsmanship.