A people set in the mountains near an ocean. They rely on farming, trade with nearby lands, mining, hunting animals or monsters, general living off the land (tanning, butchery, crafting and cooking, etc.) Technology is very intuitive and practical but primitive in the sense that there are no electronics.
A possible exception would be the rare individuals who understand science on a high level. But authorities, cost, and sake of preserving culture prevent it's being implimented very much. It may not even be more than a rumor or idea in some lands.
The monsters would be created by such rare scientists, especially those who specialize in chemistry, bringing together potent herbs and modifying them to alter bugs and animals of the world, morphing them into strange creatures for the purpose of the wicked to hold power over people.
Both technology and strange creatures are the result of especially intelligent individuals, most of which are abusing such skills. Some have used the power for good and through a special training you might learn how to make use of it yourself; everything from potions to electricity.
If magic exists at all it is but the superstitions of people who don't understand what science has done.
For the most part, the culture you become part of is barely or only gently touched by all such science, for good or bad. Some examples: the giant beetles used for transportation and loads, advanced healing medicines to apply to bandages, giant spiders or bugs that afflict some parts of the wild. On the rare side, the ability to infuse an electric charge within a certain kind of metal, to make weaponry that carries quite a shock. Creating a bolt of electricity that is even stronger from a device in order to electricute. Creating fire quickly and powerfully in almost any location.
the enemy and the motive.
the enemy is permitted by God to work out their evil ways for the time being. anyone killed is kept is God's memory and will be resurrected.
this world is like ours except a different potential path through history was taken than ours.
the first human couple did not sin when tempted. they were faithful. the earth became moderately filled with perfect beings. hundreds of years have passed since the beginning. however, the same evil spirit approached someone intelligent and offered him a special knowledge of something that would be later called Lucid Science, as long as that person would worship him rather than God and gain followers who would do the same.
the spirit creature's motive was to prove that humans did not need to live by morals or standards of right and wrong, or to listen to God at all, and that life would be better and more free and rewarding in that case. he was a rebel against God and selfishly desired worship of humans. he succeeded in luring the intelligent man in, and other men and women also gave into the temptation of independence and power.
however, Lucid Science was something that was soon to be taught to humans anyway. the rebel spirit claimed that it was his own originality. he revealed it ahead of the time intended in order to get worship. for a time, it was only used for evil.
then, at God's time, it is revealed to a limited number of humble men, including Arian - you. you are also allowed to pick certain individuals to share it with. your permission is to help undo some of the wicked until God's time to completely remove the original rebels. the waiting time is simply to prove the point that independence from God and selfish motive only brings harm and misery to everyone, even the wicked themselves.
whether God called you to this island or simply used you as a worthy tool for his will being you were in the right place and the right time, no one knows. mostly likely the latter.
imperfection did spread because generations of evil have influenced people's attitudes to varying degrees, whether or not they fully support the rebels. you were raised by parents who began to support them and you wanted to get away from the selfishness. you are not perfect because of that, but you desire what is good and right.
it is rumored that perfect individuals may still exist, untouched by the spread of evil, but even if such ones exist they are too humble to say so, and probably cannot be sure in any case.
so your getting away from the attitudes of a bad people was clear evidence that you were the sort God wanted to use in his purpose. although you may have wanted to escape to this island for partially selfish reasons, to find love, you had very good intentions to help others as well.
most of the game and story does not heavily expound on all of this background, but is gently guided by it. also similar to reality, many people in general don't even understand or think a lot about the big picture. they think it's just a matter of some people being good and some bad.