"May I dissect your brain?"
While this Promestein is technically Promestein, it's worth noting that she is NOT the same one from the original trilogy. This Promestein comes from a timeline where Ilias was able to defeat, and annihilate Alice the 1st including the Six Ancestors, thanks to the Seven Archangels. Whereas in the original trilogy, Ilias had forced Alice to seal herself and the Six Ancestors, or Ilias would destroy the world.
Promestein is first encountered in the second Tartarus.
While exploring the Tartarus, the group arrives at the doorway to the next dimension. Since Luka has the power to travel between dimensions, he need only touch it for the door to open. Something a mere human shouldn't be capable of doing in the first place.
Heading through the door, and the party is back in Remina. A figure wearing glasses, with red hair peeks out of the house on the other end of the street before rushing back in again.
They investigate the home, where they find a younger Promestein. Luka inquires what Promestein is doing here, but she asks what year it is instead. Luka tells her that it's Johannes 1455 where they come from, and Promestein notes that she must be quite some time behind them. She explains that she unintentionally teleported herself into this dimension while testing the reactions between holy and dark magic. She's been stuck in this dimension ever since. Luka promptly asks if she caused the Great Disaster, but Promestein tells him that her small experiment shouldn't have been able to cause something of that magnitude.
Ever since she arrived, she's been studying Remina and conducting more tests, making equipment out of the resources available to her. Sonya mentions that she must have been here for a long time. Promestein replies she's been here almost 200 years.
She asks how Luka managed to replicate her experiment, and if he can provide details on it to help her research. Ilias explains that there was no such experiment. Luka has the power to travel between dimensions. Promestein says that it shouldn't be possible for a human to do that and asks Luka if she can dissect his frontal lobe to find out why.
Luka declines for some reason.
She suggests making a clone out of him as an alternative, so she asks Luka to ejaculate into a beaker, which he also declines to.
You can recruit Promestein here. She reassures Luka that there shouldn't be any noticeable side effects from losing a piece of his frontal lobe. She joins the party as an excuse to investigate Luka further. Promestein still hasn't figured out who Ilias is, either.
Looking through Promestein's notes reveals some of the numerous breakthroughs she had while studying apoptosis. She learned that it is a phenomenon that occurs wherever chaos is. It transforms the inhabitants of that dimension into apoptosis beings, meant to repel foreign invaders by erasing them. However, some of the apoptosis beings retain their memories.
Assuming you recruited her, there is a side quest in the Ancient Temple Ruins devoted to Promestein and Hild.
The technology within the temple several hundred years ahead of the technology of the paradox world, much to the fascination of Promestein.
Within the temple, they come across a terminal. The group discover that when this research facility was abandoned, the previous owners erased all of their previous records, explaining why Hild possesses such little intelligence. They likely deleted most of her memory before leaving the lab. The only thing she remembers is that her master was the most important person in the laboratory.
Ilias asks Hild whether or not there is a possibility of Promestein being her master. One from another dimension. Hild confirms this is incorrect, as her master was completely different compared to the description Ilias provided of Promestein. The fact it wasn't Promestein disturbs Ilias, as one of the creatures, XX-7 is one of Promestein's creations. But that's not to say Promestein didn't work with the scientists.
At the second terminal, they find information on apoptosis, confirming the scientists working there are aware of chaosization. Like the previous terminal, what they discovered has been erased. The only information remaining is regarding Hild. It confirms that Hild was created to battle with apoptosis. She has a holy and dark fusion core, as well as the body tissue of apoptosis beings built into her. Hild confirms that she remembers her master telling her that she would awaken when the world ends. They kept her in the pod in a hibernation mode, until that happened. Strangely enough, it was Luka who awoke her.
Despite her numerous combat functions, Promestein believes that Hild was not built exclusively for warfare; otherwise, she wouldn't possess an advanced reproduction system or such advanced emotional processors. Also, she shouldn't be so stupid to the point she answers 87+65 as 142.
At the third terminal, they discover the exact date, time and coordinates of where Promestein was sent to the eastern Tartarus. The same day she supposedly did the experiment. The fact the lab administrators had access to this information confirms that it wasn't Promestein's experiment which sent her back in time, but this device. While it was her experiment which created the crack in spacetime, it was the lab administrators who set the coordinates to Tartarus. If it hadn't had been for the device, she never would have been pulled through the rift. But combining divine and dark energy is the key to creating these cracks in spacetime.
Ilias is confused why they would want to send her through one, but she has no idea. If they had just wanted her dead, throwing her into another world would have been a waste of resources. She hypothesises that they perhaps sent her through to join Luka when he passed through there. At a particular time on his adventure.
At the final terminal, is Hild's capsule. Within the capsules data, Promestein finds that Luka's biometric data had already been integrated into it, explaining why Hild woke up when Luka touched it. But only Luka's data was integrated to wake her up. No one else. Ilias inquires whether Luka is familiar with the ruins at all, but he replies he's never heard of it in his life.
Promestein brings up that Ilias has been referring to the laboratory as ruins for a while now, but that is incorrect as this scale of technology never existed in those times. However, compared to the technology in the Tartarus which appeared out of nowhere, they are very similar. Promestein believes that this laboratory came from a parallel world, and asks Hild what the date is according to her data. She responds that it should be 1543, but has configured it to 1455 since waking up. Meaning that Hild is 88 years ahead of them.
- Do you remember White Rabbit mentioning those Luka clones in Iliasburg? "Despite being flesh and blood, this Luka is sharp. Different from the specially-made ones for sure." The Luka who provided the genetic information was either of these specially made Luka's or one from a parallel world. But I have a feeling it's one of these 'specially made Luka's', meaning that White Rabbit is connected to this technology faction.
- Promestein is so far the only companion who permanently changes position in the Pocket Castle.