Swordfighter is a Mii from the Switch.
Swordfighter originally appeared as the default Mii for the Mii Swordfighter fighter in Super Smash Bros. Ultimate. He hasn't appeared in any game since. His Mii data file filename is mii_swordsman.bin.
His Mii name in his Mii data file is けんじゅつE, which translates to "Kenjutsu E". Kenjutsu being the art of sword fighting, it's only fitting. The name Kenjutsu could also be a reference to the fact that Ken- is a common name starter for males in Japan. While the "E" part is currently unknown, this means Swordfighter's name is Kenjutsu. Despite this, the name on the Mii Library is still his title ("Swordfighter") as this is what he is called in-game and this is information is only known through unused Mii data file info.
His Mii ID is as follows: AA 23 0D CE 53 8D 4A B7 84 54 F6 84 7D 4B EE 68
As he is a Smash Bros. character, he has very high quality promo art of his character render, as seen on the left. In Super Smash Bros. Ultimate, he is considered fighter #52.
He is one of few Miis that have a voice actor. In Super Smash Bros. Ultimate, Mii Swordfighter can choose from 12 different voices, all voiced by Yūji Kishi, Takashi Ōhara, Ryōtarō Okiayu, Michihiko Hagi, Hideo Ishikawa, Kiyoyuki Yanada, Umeka Shōji, Ayumi Fujimura, Makiko Ōmoto, Minami Takayama, and Kimiko Saitō.
Outside of the above Smash Bros. character render, Swordfighter unfortunately does not appear in much else promo art, aside from the large murals featuring all the characters in the game. There are some promotional screenshots of the Mii Swordfighter, however, as shown here. For some images, you may have to open them in a new tab to see the whole render.