A common isekai trope, the kingdom performing a hero summoning and you're one of the four heroes being summoned.
each summoned hero has different class privilege, and you're one of the following class.
- hero with Jack-of-all trades ability
- magic specialty
- healing and status buff specialty
- infiltration and assassination specialty
all four of you agree that you don't like the kingdom and planning to destroy it, so how would you go about it?
pick the class and make up the circumstances the way you like it.
Ai-chan wouldn't need superpowers to bring down a kingdom, but having it is nice. So Ai-chan chooses number 3, simply for personal safety.
A kingdom runs on several things:
1. Economic stability
2. Political stability
3. Public sentiments
4. Cultural identity
5. Perception of military might
6. Perception of government power
If any of these are weak, the country would fall. If more than one of these are not up to par, the country would fall.
1. Economic stability
To ruin a country's economy, create an abundance of something very essential, such as wheat, brick or iron, though this works best for something you can't export, such as houses. The bubble of abundance will continue to grow to the point that the item is so cheap, it becomes unprofitable to produce it. To the point that you can get it for the price of almost nothing. This would mean the industry for producing that item in the country becomes non-existent due to the cheapness of the item. Do this with a couple other essential goods. This creates unemployment.
Then when the bubble has grown so much that people has moved on to other things dependent on these cheap items, such as grinding flour in the case of wheat, take all the wheat away. Burn everything in the granary, burn the whole wheat fields, destroy all the farming machines. Now all those flour mills have no raw materials to work with. The kingdom has to import wheat at a huge markup, because merchants outside the country knows this is a major ching ching moment. The kingdom's finances suffer greatly, but that's not all. If wheat is the main food ingredient, now the people is hungry and resentful of the government. Of course, this is a long game, so if you want to destroy the country in just a year, this is going to take too long for you.
2. Political stability
To ruin the country's political stability, you need to look at the country's political system first. If it's a monarchy, obviously the weak point is the inheritance system. To destroy it, you need to create turmoil in the inheritance system. You can for example, support a weak candidate or support the strong candidate. Why would you support the strong candidate? By supporting the strong candidate, you get in their good books, and you can slowly put your poison in his circle. Make his circle dependent on you, to the point that losing your support is equal to losing everything. You make yourself an essential person in that circle. You make everyone indebted to you. Of course, this carries the risk of assassination, so don't do this alone.
If it's an imperial system, the local rulers generally have greater power as they obey the emperor. While the weak point in the system is the emperor himself, the large autonomy that the local lords enjoy is a much bigger weakness. If you control the emperor, you may control the empire as a whole, but the local lords will not obey you and you will stick out like a huge nail. So take control of the local lords, either by bribery, corruption, debt or blackmail. Then organize a civil war. Regardless of the outcome of the civil war, you have succeeded in weakening the empire. Yes, the outcome of the civil war is not important. It's the civil war itself that matters.
3. Public sentiments
To ruin public sentiments, all you need to do is ensure that they think the government is unjust, cruel or highly corrupt. You can do this in many ways, such as bribing the official to let known criminals go, give them an incentive to look the other way while a crime or cruelty is being committed, get them to go elsewhere as your bandits raid and plunder a region or manipulate events so that innocent people are punished for things they don't commit.
While these won't automatically make the people revolt, and you don't want them to revolt, at least not just from this, it plants the seed of revolt. Why do you not want them to revolt? Because this revolt would be weak and barely of any consequence. The government will send soldiers and the revolt will be quashed, everyone gets executed, the end. You want the dissatisfaction and anger to simmer, to grow, and you need two other factors removed before they can revolt.
4. Cultural identity
To ruin cultural identity... well, there's no quick way to do this. But there are basically two things you can do. One, immigration. Two, religion. The problem with immigration is that you need to convince a lot of people to move to an area at a given time, so that the majority of that region's population gets diluted by the people who moved to that area. China is doing this in Xinjiang, by sending lots of Han ethnics to Xinjiang to dilute Xinjiang people's majority, thus eventually making the Han ethnic a majority or almost a majority. If you have the means to do it, you can even sterilize the local population so that only the immigrants can breed, such as what USA once did with a vaccination drive on the black populace.
The second option is religion. If immigration is not possible, then the only other choice is for you to convert the locals into another culture. There is no easier assimilation than religion. Muhammad created Islam to completely subvert the local Arab culture which was admittedly horrible, where daughters were buried alive for fear that they would be used as a hostage. This immediately caused several civil wars, which for a time, weakened the Arab tribes. Had there been anyone interested in the land at the time, this would've been the prime time for invasion. However, nobody wanted a piece of land that has nothing but sand. In Japan, this also happened, where the Jesuit priests were preaching and converting the populace into Christianity which was not only a proselytizing religion, but also a religion that clashed very badly with Buddhism and Shintoism. Tokugawa was afraid that if Christianity spread even further, the Christians would start demanding special rights or worse, bear arms against the Bakufu, so he outlawed and persecuted Christians to reduce their number.
5. Perception of military might
To ruin perception of military might is easy. Get rid of their military. You can play the long game of fighting on your own to the point that the military pride is gone and the army is just sitting around playing cards when they should be training for war. You will then get a bunch of pansies joining the army just for the cushy job of being paid to do nothing. Over time, the government will start cutting military budget as you alone is enough to deter all possible threats. This may take years, but what happens next will make you laugh. Announce to all countries that you're retiring and immediately disappear without warning. Nobody expects the Spanish Inquisition, but for this kingdom, they will never expect the numerous invasions and bandit raids that come to them shortly after you 'retire'.
Or you can play the short game, which is to create a shortage of weapons by providing inferior weapons to the army. They will keep buying more weapons, but if you provide inferior ore, they will still still get inferior weapons. If they use iron or steel, all you need to do is add sulphur. Or you can weaken the military itself, you have magic, use it at the right time, such as when they're fighting. The more they lose a fight, the perception of military might gets lower and lower. Bandits appear more, foreign countries do more to test the water. At some point, invasions and raids become a daily occurrence that the military can't keep up with, even if they manage to repel most of them. It's just a downward spiral.
6. Perception of government power
To ruin perception of government power, it's fairly simple, but it is a long game. You just need to convince the populace that the government has no power to affect change or carry out reforms or their own orders. This was what happened to the Holy Roman Empire and the various Chinese dynasties prior to the Qing. In the Holy Roman Empire, the electors had so much power that the candidate for the emperor had to keep giving them land and additional privileges just to get support to the point that the emperor ended up with no power, no land except for the capital and no money. They had to rely on the donations by the various nobles that were richer than the Holy Roman Emperor. As the issue spirals further, the various nobles received even more privileges, such as knighting their own nobles, full control over taxation and full power to design their own laws. If they want to break away, the Holy Roman Emperor had nothing to stop them with. He basically had his castle, that's it, and that's not even entirely his castle anymore.