artoria_pendragon_(swimsuit_archer)_(first_ascension)_(fate)
Artoria Pendragon Swimsuit Archer in her First Ascension swimsuit from Fate/Grand Order. She wears a white bikini with a blue criss-cross halter and bows on the bikini bottom.
Note that this looks extremely similar to an official alternate swimsuit that she's seen wearing in Fate/Hollow Ataraxia (post #2095987). This Ascension is most likely an adaptation of that bikini.