The Rance Series has a pretty complex background to it's setting that makes it something very unique in the fantasy genre. This page is meant to explain the series' background and mechanics for unfamiliar players. This is by no means a deep dive of series lore, but it will hopefully answer the question of why the setting is in the bleak state it's in. For further questions or in-depth information on specifc characters please refer to the Alicesoft wiki.
The Planner Scenario
The Planner Scenario was designed to turn the world into a soap opera of endless conflict for the supreme god Ludo-Rathowm. A major part of it is the existence of monsters who exist for the sole purpose of making life hard for humans. The true threats of monsters are the fiends and their leader the archfiend. They are invincible under most scenarios and can easily devestate whatever humans they come across. The real-life RPG mechanic of characters leveling up as they defeat enemies is a part of daily life in Rance's world but there's a twist to it. Instead of having a level cap of 99 or higher, the average human caps out around level 8. Imagine, if you will, an RPG where you stop gaining experience after level 8 and have to play the game normally. It makes for an interesting twist on established tropes which is the point of Rance's setting to begin with. In addition to level caps the Planner Scenario also introduces skill levels which further limit humanity. They apply to all sentient beings and decide what they're innately good at while at the same time limiting their potential to grow. These skills can go from levels 1 to 3, 1 meaning you're a prodigy, 2 meaning you're a genius in the field that will go down in history, and 3 meaning you're one of the strongest practitioners of this skill that will ever exist. It goes without saying that beings possessing a level 3 skill are practically nonexistent.
The Hero System
The Hero System is a major part of the Planner Scenario that exists to keep the monsters from wiping out humanity and ending the eternal conflict between the two. A "hero" is chosen at random from humanity and serves for 6 years between the ages of 13 and 19. As soon as they turn 20 their powers vanish immediately and another hero is chosen. While someone is the hero they will have perfect luck and be given a magical sword that becomes stronger the more humans die, ultimately giving it the power to break the invincibility of fiends and kill them. The hero's goal is to kill the archfiend and save humanity from the monsters wrath for a short while. While their job is important it's a futile effort that continues a vicious cycle of suffering across the world.
Fiends and the Archfiend
An archfiend is the ruler of monsters chosen when the previous one is unable to fulfill their duty. While in most cases their reign ends with their murder it can be a result of age, since an archfiend is meant to serve 1000 years before finding a successor, being given a small amount of leeway after this time if they haven't found one yet. No matter how virtuous a being was before becoming the archfiend they will eventually fall into a bloodlust that can only be sated with the massacre of humanity. Due to the innate invincibility of fiends this massacre is the only way they can be stopped, as it will ultimately empower the hero, starting the cycle over again on their defeat. The archfiend can feed it's blood to sentient creatures and turn them into a fiend. Fiends gain the invincibility of the archfiend along with a significant boost to their strength but they don't lose their minds like the archfiend does.
Major Races in the Rance Setting
Humanity is the protagonist race of Rance's setting and the primary target of the chaos created by the Planner Scenario. They weren't the original target of the Planner Scenario, those were Round Ones, a species of monster that isn't especially dangerous or powerful. Kalars are a race similar to elves in other pieces of fantasy fiction, the twist here is that they're an exclusively female race that relies on imprisoning human men to bear children. Haniwa are a race of sentient pottery well known for the ability to completely negate any magical damage inflicted upon them as well as their unique tastes. Dragons existed around the time that Round Ones were the target of the Planner Scenario and they were just as powerful and intelligent as they're often portrayed in fantasy media. For this reason they were hunted to near extinction on the orders of the supreme god and now a precious few remain, all living in hiding or reborn as fiends.