Marianne is a Mii from the Switch.
Marianne originally appeared as the default Mii for the Princess role in the files of Miitopia (Switch, Demo), but unused within the demo itself. She later appeared in the full game of Miitopia (Switch). Once the player replaces her with a Mii of their choice, Marianne would never appear again, unless that Mii is deleted. Her Mii data file can be found in \cmn\storedata\npc_default_mii.sarc and is named Castle00_Princess00.charinfo.
Her Mii name in her Mii data file is ひめk, which translates to "princess k". Her height is set to 93 and her build is set to 0 (minimum). Her Mii ID is as follows: 78 A7 E1 1F C7 09 40 73 8F 84 3F C5 E9 03 55 4A
Her Mii data file does not contain any unused Mii data.
Marianne's role in Miitopia (the Princess) is described as so:
She seems to bear resemblance to a Mii featured in Miitopia (3DS) promo art, 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 Marianne and the promo art Mii are meant to be the same character.
The names of the default Miis in Miitopia Switch often vary drastically depending on region. Marianne's name on the Mii Library is going off of the US English version, for consistency. A chart containing all of Marianne's names is located at the bottom of this page.
Marianne appears in promo art for Miitopia (Switch) as her in-game role, the Princess.
Below is a screenshot of her in-game as her role in Miitopia.
This Mii originally appeared on the Switch!
Here's how to recreate them on the Switch:
Names in other languages
Source: Miitopia (Switch, Demo)