Poko, as is mentioned in her background, is from an extremely isolated remnant of the ancient civilization. Nowadays, they refer to themselves as Yeftbu. Taking from the system they had before the collapse of the ancient civilization, they are a monarchy. Although he does call himself king, the way he lives and the amount of people he rules over would make him more akin to a chieftain. Their technology has regressed with time, the people who actually knew how to operate and maintain such things never making it to this place. There's still some old pieces of ancient tech around, but are regaled as artifacts and are not to be used. The ancient weapon, the Dragonator, would have been really helpful during the battle with the Wurm that ravaged their village, but alas, the king is kind of a tool and had sealed away the artifacts years ago so that they would not be able to be stolen.
The village they all gather in has no official name, just referred to as "the village" in their tongue, but if you asked Poko, she'd probably make up a name on the spot like Yeftbu Village. The wildlife and plant life of that underground society is kept alive through ancient magic still operating a sun-like light that bathes the whole area in magic that accelerates growth. This was to help keep them alive and well fed, as the Yeftbu are much larger than Pen (with Godfred being an especially tall specimen). Over time, though, the magic caused the vegetation and wild stock to mutate, growing too large too quickly and they have spread all across the area, turning it into a jungle filled with unique flora and fauna not seen anywhere else in the world.
Even with their size, the animals there are not particularly dangerous compared to real monsters, which is why the Yeftbu were taken so off guard when a Wurm came bursting through the walls of their enclosed world. It was only because of their large size that the Yeftbu were able to defeat the Wurm. The village has your typical hunter/gatherer systems put into place, with other jobs being available if you specialize (shaman, clothmaker, and whatnot) with the exception being to royalty. The king believes himself to be descended from royalty of old (he isn't) and is in charge because God deigned him to be. Like I said, a tool. Unfortunately for him, the recent event with the Wurm has caused the villagers' opinion of him to sour quite a bit. Already there are hushed talks about getting one of his children to take his position.
Speaking of gods, the Yeftbu praise the goddess Ovold, a deity of light and growth who's name has been passed down even before the destruction of their old civilization. They are attributed to the creation artificial sun that was actually made by their ancestors in centuries past. The light itself is mistakenly thought of as Ovold's shining presence and the practice of offering it mana in worship has kept the night/day cycle and the magical fortifications to the walls surrounding the area going even after so long.
In years past, children dying was quite common. It is believed by the Yeftbu that the young are often targeted by the enemies of Ovold. As such, a practice of adorning the clothes of children with a sun and little dolls blessed by the shaman was started. The adornments act as guardian spirits to protect them until they grow strong enough to fend for themselves. In reality, the reason children were dying was because the Yeftbu had not figured out how to properly prepare meals made from the unique flora and fauna of the area. Foodborne illnesses were much more common then, but have since been reduced majorly. Even so, every child still walks around with suns and dolls sewed to their clothes until they reach a certain age.
The staple food of the Yeftbu is the Kovo Plant, mostly because of overabundance. It's a leafy vegetable that puffs up to thrice its usual size when wrung of its juices and let dry. Commonly sliced and served as the main part of many meals, the spicy and slightly bitter Kovo Plant is an acquired taste to anyone who didn't grow on the stuff. The combination of edible plants growing everywhere, oversized wildlife, and water elementalists throughout the village has allowed the Yeftbu to never have to worry about where their next meal is coming from. There's always been plenty to go around.
Although they do not lack in food, something that is almost absent from the area is any kind of workable stone or metals. As such, it is very common for the Yeftbu to use bones and wood to make their tools and utensils. While easily achievable thanks to the large bones from the wildlife around them and the abundant plant life, they are not strong enough to be that reliable. They have been unable to mine the stone walls, unaware that they have been supplying the mana to keep them fortified. To make up for that, they have become very skilled in their woodworks.
Magic is not very uncommon among the Yeftbu, with water elementalists being the most common as they are needed to maintain drinking water levels. While other magics are around, the most prestigious of them is the ethereal magic performed by the village shaman, casting blessings and healing when medicine doesn't work. However, the strength of the magic in the village is quite lacking overall. Even so, most sorcerers in the village are highly regarded as their role is seen as necessary. The practices of the water elementalists and the shaman are handed down every generation, usually to whoever has the most potential. Other sorcerers can't be that picky, so they have to choose an apprentice from whoever is interested, typically their own children.
Their language has changed a bit after having been holed up for so long, but not enough to be unrecognizable if you knew the original language. It would just sound like a really harsh accent. A bit of a meta note, but when making words in the Yeftbu language, I translate it into Portuguese and then put the sounds of that word through a Cherokee syllabary I found. I then write out the letters into similar-looking English again, adding vowels when I need to make the word sound more pronounceable. For example, "Ovold" is just "Sun" put through my inane system.
Poko is the king's fifth daughter, the eighth and final child. He would have more, but he's gotten too old now, so he's shooting blanks. Even if she is technically royalty in the village, she isn't treated like it, nor does she want to be. As the eighth child, she is basically written off completely and is free to do what she wants by her parents. Similarly, she doesn't really have any overly deep connections to her siblings. However, that also means that she lacks certain guardianship that her oldest siblings get. While she is able to go where she'd like, that also means there's nothing to stop others from hurting her. Not everyone in the village is nice, after all. She has already had a few run-ins with less than kind individuals.
With this level of supervision, it's quite easy for Poko to slip away every day and go to the surface. Even if she were gone for a night, as long as she returned, only a few questions would be asked before everything goes back to normal. If someone were to ask for her to bring them to her village, she would refuse. She is aware that her father is not a very nice person and would likely see outsiders as bad people, even if she told him otherwise. She does not want to risk losing her chance at becoming strong enough to be her village's protector. In the future, she would be much more open to it.