Promestein

Promestein is a powerful scientist with vast technology. In reality, she is an angel who devotedly follows Ilias's cause without question. She also created the Chimera at Ilias's order, and used them to cause the Slaughter of Remnia.

Promestein's personality is very calculative in nature, showing no emotion in any of her appearances and speaking very little, other than to observe others and introduce herself.

Although she has never engaged in battle once in the story of Monster Girl Quest so far, it is assumed that her power extends beyond almost all of the characters in the game, bar Ilias herself.

Biography
Promestein first appeared as Luka drags Alice out of the Haunted Mansion, bringing supplies to Chrome and helping her with her research. She recognizes Alice as the Monster Lord and leaves shortly.

She then appears again in the Witch Hunt Village. When Luka returns and heads to Lily's mansion, Promestein is there, suggesting she helped Lily with her crude experiments. She sees Luka, but leaves shortly. Luka asks Alice if Promestein is a monster, but she isn't able to trace any sort of monster blood or power within her.

In Grangold, Alice hypnotizes a female magic scientist to reveal how they detained the Queen Ant. She reveals that years ago, Promestein came to them and gave them advanced machinery, and has been supplying it to Grangold over the years, however she had stopped coming recently. Later, Luka asks if Promestein is human, but Alice doesn't think so either.

Luka then encounters the scientist again at Remina. At first, he assumes she lives there, but realizes she may be involved in the massacre.

At the end of Chapter 2, after Luka revolts against Ilias, Promestein appears leading the attack on the Monster Lord's Castle, revealing that the Chimera were all her handiwork. Luka yells that their defeat will never happen, until Granberia and Alma Elma receives smack-downs by Arc-En-Ciel and Hainuwele, respectively, as well as Amphisbaena, Tsukuyomi, and Rapunzel; the true masterpieces of the Chimera created and modified to exploit the weaknesses of the Four Heavenly Knights. Luka attempts to attack the mastermind, but Promestein dodges using Zylphe and explains that she had analyzed and mass produced artificial Four Spirits. Alice reminds him that he's not alone in this battle, and with Angels and Chimera closing in from all sides, the angel who's mass producing monsters, plus the one pulling the strings, they charge into the fray together.

Trivia

 * Her name is a portmanteau of Prometheus and Frankenstein. This references her tendency in-story to "gift" humans with arcane knowledge in the same way Promethues gifted humans with fire, along with her and Frankenstein both being "mad scientists" who try to create life.
 * Her angel wings and halo seem to be translucent, as opposed to the other angels revealed so far. What this means for her or her character is yet to be known.
 * Much like Ilias, Promestein's motives have yet to be revealed, besides being Ilias's subordinate.