The Wado Ichimonji, for Roronoa Zoro, is a sword of great personal value and once belonged to Kuina and her kin. It is one of the 21 swords of the Great Grade as well. After Kuina's death, Zoro asked her father for it who then gave him the sword.
Appearance
With a circular hand-guard, the sword has a pure-white hilt. The sheath is painted white and the suguha or straight blade is the hardening line.
In descriptive words, Wado Ichimonji is a Katana style Shinogi Zukuri that has a conventional but still beautiful pure-white ito wrapped around a gray samegawa covering the tsuka (handle), leaving a traditional pattern shaped like a diamond. There's a pretty, simplistic kashira of the same color as the tsuba at the end. The tsuba, or crossguard, often conveys a harmony of simplicity: it consists of a thick, rounded oval tsuba through which the blade passes in a beautiful golden metallic hue. The colors of the edge are divided in complete equality to convey once more the exquisite simplicity of this blade. A deep black is the inner bo-hi, while the outer ha, or border, is a shining white. Slightly towards the end, the blade bends, with a beautiful sharp tip that slices through enemies. With a modest kojiri at the center, the sheath reflects a happy harmony, being absolutely white.
Tashigi describes it as "magnificent" when it catches her eye in Loguetown.
Abilities
Wado Ichimonji is one of the strongest swords in the world described by Tashigi, a sword enthusiast, as a magnificent katana of the highest caliber, as the masterpiece of the legendary swordsmith, Shimotsuki Kozaburo, listed as one of the 21 Great Grade swords. Most notably, it is incredibly strong, capable of withstanding strikes by the Yoru of Dracule Mihawk, a Supreme Grade sword that shattered his other two arms, cut massive battleships, and a giant iceberg; it could also protect for a period of time against strikes by another Great Grade sword, Shusui, wielded by Shimotsuki Ryuma. These are remarkable feats because Yoru and Shusui are famous black knives, and at that time Wado Ichimonji was not imbued with Haki.
For this very sword, Tashigi of the Marines was chasing Zoro because she couldn't tolerate the fact that a pirate is in the possession of such a famous blade. However, although he has allowed others to study it, Zoro refuses to ever give anyone this blade. The fact that Zoro used it for his Ittoryu Iai: Shishi Sonson strategy against Mr. 1, cutting through his steel body, further shows both its strength and sharpness.
When using his Santoryu, Zoro tends to put Wado Ichimonji in his mouth, while he uses it when using his Ittoryu in some battles before the time-skip. He tends to favour Shusui when using his Ittoryu after the timeskip.
Since Wado Ichimonji was forged alongside Enma by Shimotsuki Kozaburo, it was able to allow Zoro to get used to Enma quite quickly somehow.
Past
Sometime in the past, Shimotsuki Kozaburo developed Wado Ichimonji. He took his handcrafted Meito sword with him when Kozaburo left Wano. The sword was carefully stored in the Isshin Dojo warehouse, seldom used as Koushirou had no need to use it for fighting because his dojo used only wooden swords to train his students and teach them. Roronoa Zoro, a pupil of the Isshin Dojo and a competitor of Koushiro's daughter Kuina, once challenged the girl to a real sword fight. For this battle, Kuina then borrowed Wado Ichimonji.
The sword was in the hands of her father, Koushirou, following the death of Kuina. Zoro told Koushirou that he would become the world's best swordsman, and asked for a blade. Koushirou acknowledged his proposal and moved his second-best student on to Wado Ichimonji.