Copied from the fandom for your convenience:

Hilda (ヒルダ) is the leader and one of the founders of Amnesia, creating it under the belief that In-Births like her deserve to use their powers freely. She serves as the secondary antagonist within the story.

Hilda was the eleventh character added into the original UNDER NIGHT IN-BIRTH as post-launch content, though she debuted as a boss character in Arcade Mode beforehand.

hilda_under_night_in-birth_character-appearance:

hilda_under_night_in-birth, aged_down, slim, very_long_hair, blonde_hair, red_eyes, grey_eyes, heterochromia

hilda_under_night_in-birth_standard_outfit:

two-tone_dress, mulitcolored_dress, multicolored_clothes, black_pantyhose, white_high_heels