Tag used for Mia (Fire Emblem) from Fire Emblem specifically when dressed in her swimsuit from the Fire Emblem Heroes 2020 Summer Passing banner.
Likely to be depicted with Lucina (Fire Emblem) (possibly with her mask), the secondary character of the Harmonized Unit.
Note that it's possible (especially for older artwork), to depict Mia in a swimsuit without it being the one described above, in which case this tag should not be used.
TBU