Miyu is a Mii from the Wii.
Miyu originally appeared as one of the 60 CPU Miis to be included with Wii Sports. Since then, she's appeared in Wii Sports, Wii Sports Resort, Wii Party, Wii Music, Wii Fit, Wii Fit Plus, Wii Fit U, Super Smash Bros. for Wii U, and Super Smash Bros. Ultimate. In most of these games (aside from Smash Bros.), her internal ID is 015, however in Wii Music it is 54. Her Mii data filename is cpu_mii_015.rcd in Wii Sports, mii_015.rsd in Wii Sports Resort, Wii Fit, and Wii Fit Plus, mii_015.ffsd in Wii Fit U, and is cpu_mii_db54.rsd in Wii Music. Wii Party combines all 100 Mii data files into one larger file named mii_rsd.bin in the same ordering as Wii Sports Resort. Her appearances in the Smash Bros. games are limited to prerendered 2D textures and 3D models, as shown below.
As with every CPU Mii, she has Mingling turned off. Her Mii name in her Mii data file is みゆか ("Miyuka"). In her Wii U/3DS-format Mii data file, she was originally created on a Wii (1).
Her Mii data file does not contain any unused data.
In Wii Music, her Mii data file is slightly different. While it's mostly the same as it is in Wii Sports Resort, it now includes a filled out Mii ID and console ID. Her Mii ID is 80-4f-98-9f and her console ID is c2-3d-21-af. Her Mii ID tells us she was created on August 30, 2006 at 12:01:00 PM.
According to a September 2020 Nintendo leak about CPU Miis, Miyu's nationality is Japanese (Asian).
In the files for Wii Sports, her dominant arm for Baseball (Batting) is right-handed, Baseball (Pitching) is right-handed, and Tennis is right-handed. Her unused dominant arm for Boxing is right-handed. Her Baseball Pitching style is normal. She's ranked 2 in Baseball, 56 in Boxing (meaning she doesn't appear in Boxing), and 53 in Tennis. Her group IDs are 5, 0, and 1.
In the files for Wii Sports Resort, her Wii country ID is 1, like all CPU Miis. Her dominant arm for Table Tennis is left-handed. She's ranked 97 in Swordplay, 78 in Basketball, 45 in Table Tennis, and 72 in Cycling. Her unused Canoe and Debug ranks are both 15, matching her ID value of 015.
Miyu appears in promo art for Wii Music playing the marching snare and Wii Party playing Basket Bonanza. She also appears as a flat texture in the background and as a 3D model playing Power Cruising on the Wuhu Island stage in the Super Smash Bros. games. For some images, you may have to open them in a new tab to see the whole render.
Note that in her Wii Party render, she's wearing her favorite color (purple) instead of the player color.
Names in other languages
Source: Wii Sports Resort