Louie is a Mii from the Switch.
Louie originally appeared as the default Mii for the Royal Support (Right) role in Miitopia (Switch, Demo). He later appeared in the full game of Miitopia (Switch). Once the player replaces him with a Mii of their choice, Louie would never appear again, unless that Mii is deleted. His Mii data file can be found in \cmn\storedata\npc_default_mii.sarc and is named Castle00_KingSoldier00.charinfo.
His Mii name in his Mii data file is ささえひだり, which translates to "left support". His height is set to 76 and his build is set to 28. His Mii ID is as follows: DA 90 E0 41 80 17 45 5B B0 5E 48 50 EB 2D 89 3F
His Mii data file does not contain any unused Mii data.
Louie's role in Miitopia (the Royal Support (Right)) is described as so:
He seems to bear resemblance to a Mii featured in plenty of Miitopia (3DS) promo art for the Red "Youngest Fab Fairy" Frog monster, as it seems a handful of the Miitopia Switch default Miis were based around Miis that appeared in promo art for the original game, but it's unconfirmed if Louie and the promo art Miis are meant to be the same character.
The names of the default Miis in Miitopia Switch often vary drastically depending on region. Louie's name on the Mii Library is going off of the US English version, for consistency. A chart containing all of Louie's names is located at the bottom of this page.
Louie unfortunately does not appear in any promo art. In the demo version of Miitopia (Switch), he also never actually appears in the story, and only appears once in the casting screen. Below is a screenshot of him in-game as his role in Miitopia.
While Louie himself does not appear in any official promo art, a very similar Mii does appear in promo art for Miitopia (3DS), on the face of the Red "Youngest Fab Fairy" Frog monster. Note that this monster only takes the faces of the Youngest Fab Fairy role, while Louie is the Royal Support (Left).
This Mii originally appeared on the Switch!
Here's how to recreate them on the Switch:
Names in other languages
Source: Miitopia (Switch, Demo)