Helena Blavatsky is a Caster-class Servant from Fifth Singularity, E Pluribus Unum. She is a member of the American forces serving under Thomas Edison.

Fate/Grand Order: Turas Réalta:

Appears in chapter 38.

Fate/Grand Order: Epic of Remnant II - Agartha:

Appears in chapter 36.

(Source: TYPE-MOON Wiki)