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She is voiced by Sayaka Ohara in the Japanese version of the anime and Colleen Clinkenbeard in the English version, both of whom also voice Erza Knightwalker.
Therestina is a woman with wavy orange hair which is most of the time gathered into a ponytail. She is shown to have glamorous proportions and is "well-endowed" as well. She also wears a pair of glasses.
In her office attire, she wears a dark-colored coat and a pencil skirt with the same colors. Light brown stockings and white high-heeled shoes complete her outfit.
At first glance, she seems to exude an air of elegance and authority and is also easily approachable and friendly. She also seem to be childish somewhat, having many toys decorated in her office and is fond of a specific kind of candy that comes out of small cylindrical tube where she easily guesses what color it is.
This is all a facade for her true nature: she is truly cold and uncaring of people using them as pawns for the goals at hand, she is also well prepared in situations having installed Capacity Down in a research facility in the event of espers attacking (such as Misaka Mikoto and company) as well as determining the weakness of Mikoto's Railgun. However, she is somewhat boastful of her own abilities and highly unstable, often breaking down in hysterical laughter while parading her plans when things go her way.
- Her "maniacal laugh" in the last few episodes of Toaru Kagaku no Railgun has been compared to Beatrice in the anime adaptation of Umineko no Naku Koro ni. Coincidentally, Sayaka Ohara, who Therestina in the Japanese version, also voiced Beatrice, who shares an equally twisted attitude. However, Therestina is a Complete Monster, while Beatrice is more of an Anti-Villain.
- She also looks very similar to Margery Daw from Shakugan no Shana. Coincidentally, Colleen Clinkenbeard voices Margery in seasons 2 & 3.