Part 1: Is Shanks a Swordsman?
In the manga, vivre cards, databooks, etc Shanks has been confirmed to be a swordsman various times. For example, this databook calls him a “swordmaster”
We know “swordsmaster” = swordsman as Zoro is stated to be a swordsmaster and that Mihawk is waiting for a “swordsmaster” to surpass his rival, Shanks.
Another source calls him a “Great Swordsman” when referencing Mihawk’s visit to Shanks, which proves that Shanks is a extremely strong swordsman and not just a guy who happens to use a sword.
本来左ききであるシャンクスはかつて、右の腰に長剣を携えていた。ミホークとライバルだった過去からみても、その剣の実力は世界でもトップクラスだったのだろう。 Shanks, who is left-handed by nature, used to carry a long sword on his right hip. He must have been one of the best swordsmen in the world, given that he and Mihawk were rivals in the past.
Furthermore, in Novel Zoro where Marines are in a bar discussing who’s the strongest swordsmen, 5 candidates come up. Mihawk, Zoro, Vista, Ryuma, and Shanks. This means that even in the One Piece World, Shanks is considered a swordsman.
When comparing Mihawk to Shanks, the Marines mention SWORDSMANSHIP, which heavily implies Shanks is a swordsman as that’s the main factor they’re using. In another way to say it, the Marines wouldn’t say “Mihawk is a better swordsman than Kaido” when comparing the two as Kaido isn’t a swordsman, making the point irrelevant.
And for the final confirmation, the SBS Art. Many people misinterpret this and say “It’s a fanart, so it’s not official” which is wrong. The ART itself isn’t made by Oda, but the STATEMENT REFERRING TO THE CHARACTERS AS SWORDSMEN is made by Oda, which is what matters. To explain it better:
FANMADE – THE ART ITSELF
STATEMENT COMING DIRECTLY FROM ODA – THE STATEMENT CALLING THEM SWORDSMEN
Raw Japanese Kanji: 剣士勢揃い!!斬れると痛エぞ~!? Translated: “The swordsmen line-up!! Getting cut by them hurts!”
PART 2: Swordsmanship Skills
Mihawk is a greater and more skilled swordsman than Shanks, not much more needs to be said. I’ll leave all the evidence here to make it absolute, however.
Raw Kanji- “背に持つ巨大な黒刀と、鋭い鷹の目が世界一の証。ゾロの中に本物の強さを感じ、その成長に期待をかける” With the giant black sword on his back and the sharp eyes of a hawk, they are the proof of the world’s best. He senses true strength within Zoro, and has high hopes for his growth.
Raw Kanji- “剣の道の頂に、長年に宣り君臨する男!! 最上大業物12工の一振り「夜」を背負い、王下七武海の一角として、単身海賊達を狩り続ける。ミホークの退屈な日々に終止符をうつ挑戦者は、いつ現れるのか!?” The man who has reigned at the peak of swordsmanship for many years! Wielding one of the 12 Supreme Grade Swords “Yoru”, he hunts down every single pirate as part of the Seven Warlords of the Sea. When will a challenger appear before Mihawk to end his boredom!?
