Meiou-sama ga Tooru No Desu Yo

"--You tried to kill me, you guys are bad."

Meiou-sama ga Tooru No Desu Yo (冥王様が通るのですよ！aka Make way, Meiou-sama Coming Through!) is a web-novel, adapted to manga, written by Nan Kikuchi and illustrated by Toma Yugimaru.

The story follows protagonist Osamu Takamitsu who suffers an extremely rare disease (to the point that only six people out of the billions on Earth suffer from it) that is completely asymptomatic and undetectable, until his organs just decide to malfunction, completely at random. Despite the best doctors and nurses working on him night and day and him spending his entire life in the hospital, he dies during a random flare-up, right in front of the nurse while "ghost-hunting" after hearing rumors about how the hospital is haunted...

Osamu soon wakes up, having reincarnated as a spirit in another world, and decides to reinterpret the kanji of his name to call himself "Shu Arclight." Even though he only retaliates when someone or something tries to kill him, never being the one to initiate hostilities, he still has to wander from place to place to avoid being hunted, until he meets the female protagonist, Iris Silverbread, saves her life, and teaches her how to use magic in exchange for her teaching him about the common knowledge of the world. When the Holy Kingdom of Ramza ignores Iris's warnings to leave him alone, unilaterally declares her a traitor, and drags her off to the royal capital to burn her at the stake as a witch, that's when he takes it personally and declares war.

Tropes used in Meiou-sama ga Tooru No Desu Yo include:

• Circular Reasoning: How the church's racism justifies itself. Whenever a "demon" is found doing something sympathetic, such as rescuing a lost child, or even teaching an apprentice how to use magic, the child/apprentice the "demon" is protecting is declared "corrupted" and attacked, or the so-called demon is accused of faking it and attacked. When the demon so much as puts up a shield in self-defense, the attacker cries out "See! Demons are evil!" and thus anyone on the fence immediately sides with the attacker and anyone opposed to the fight, for whatever reason, is declared heretical, executed, and then the facts are hidden from the public.
• Crapsack World: In addition to all the horrors of a pre-industrial medieval society, such as poor hygiene, rampant poverty, crime, disease, and a church that scapegoats "foreign" influences to keep the populace pacified, monsters roam the lands and graveyards are dangerous as undead roam them at night, meaning burials have to be done quick, and practitioners can't mourn their loved ones very long. The best the holy knights can do is to keep the undead contained to said graveyards. And having the undead's numbers fall isn't good news. Because it usually means that something even worse has decided to make that graveyard a nest.
• Create Your Own Villain: The Church of Demonism, and the country of Grenier that houses it, have a very strong tendency to push people into becoming the very "evil monsters" that the church crusades against. Shu Arclight is not the first, by any stretch of the imagination, and is clearly not going to be the last, not until the very church itself ceases to exist, a goal Shu Arclight clearly strives for.
• Crime of Self Defense: Shu Arclight earns the enmity of the Ramza kingdom because he dared to fight back when people unilaterally decided to attack him with deadly force, and a crew of self-righteous "holy knights" decided to raid his home village, laughing like loons, as they butchered every living thing, including unarmed and helpless women and children. Even then, he was content to retaliate only against the perpetrators. It's when Iris went back to her superiors, warning them that Shu is way, way too strong for them to deal with, and they'd best be served by leaving him alone, a favor he'd promised to happily return, only to be ignored, sentenced to die as a "traitor" and burned at the stake as a witch that he took it personally and declared war. Even Iris gave up on the kingdom at that point.
• Cycle of Revenge: By the time Volume 7 rolls around, the Church of Demonism, extremely self-righteous and corrupt, has long, long ago intentionally deluded themselves into forgetting that they started the fight with Shu Arclight and Iris Silverbread, by attacking without warning nor provocation, prompting the two main characters to retaliate, and demand revenge for their fallen as a result of said retaliation...
• Digging Yourself Deeper: On a national scale! Thanks to their own Fantastic Racism, the church of Demonism, run by the country of Grenier, believes the only way they can prevent the prophecy of a "Demon King" ending humanity is to launch a preemptive attack against where the "king will be born" thus eliminating him before he gets the "king" title and is too strong to stop. So they launch an attack on the village of the suspected "Demon King" Shu, who retaliates with lethal force, wiping out the knight order, save Iris, who goes back and pleads with her superiors to stop the attacks, citing that Shu has promised to stop retaliating if they leave him alone. But because "demons are always evil" they brand Iris a traitor and send her to be executed, as they gather reinforcements to try again. This prompts Shu to rescue Iris wiping out the royal capital out of revenge for his subordinates and going after his disciples, but even after he carries out his threat, the top brass still goes out of their way to try to subdue him at all costs. This prompts the oracle who keeps getting the prophecies that subtly warn humanity of the danger to kill herself out of guilt.
• Empire with a Dark Secret: Several. Not only does the empire under the sway of the Church of El Magio have a tendency to persecute "heretics" and then make the actual events top secret while making the official version scapegoat the "demons" somehow, but the empire the protagonists flee to has a policy where they prop up the brutal and corrupt governments until the citizens can't take it any more and rebel, then use the rebellion as a pretext to invade and take over, while keeping the rest of the continent in the dark. The Real secret though humanity used to have even more impressive magical technology, but lost a war with five "Demon Kings" and fled to another continent, taking what bits and pieces of magic tech they could with them. The Church of Demonism has spent centuries trying to unite humanity under its umbrella to try and take their native lands back, with the intention of making up the shortfall in martial and magical might with raw, unbridled fanaticism.
• Evil Versus Evil: Starting in volume 3, the greater conflict involves two dystopias duking it out. Which suits Shu and Iris just fine as it provides Shu with plenty of opportunities for wet-work, where he excels, and since they're both rotten to the core, it doesn't ping Iris's conscience when Shu has to go to work, no matter who his targets are.
  • The former is the theocratic dystopia featuring the Church of El Magio, aka Demonism, and its vassal states. On paper, they practice "all humans are created equal" and practice egalitarianism. In reality, they are fanatically racist, force any and every mage worth their salt into the military, and respond to any disagreement with the official doctrine, no matter how justified, by going wild-eyed, foam at the mouth, murder-crazy. Which is what drove Shu and Iris to villainy in the first place.
  • The latter is an empire built on a false meritocracy. Yes, their mages have more freedom to determine their fates, and they preach that the strong and talented will rightly be rewarded for their hard work. In reality, they abuse their vassal states by propping up corrupt and oppressive regimes until there's a revolt and then move in their armies to loot and plunder under the pretext of "restoring order," exploit uneven trade deals to squeeze said vassal states dry, and even in the empire proper, at best, turn a blind eye to the strong exploiting and abusing the weak.
• Fantastic Racism: The Ramza kingdom's Church of El Magio preaches that "demons" like Shu and monsters are Always Chaotic Evil and deserve extermination without question, while humans are a mix of good and bad. While there are hostile and mindless monsters, that narrative is just not true. There is, supposedly, a minority sect that questions it, since some monsters can also use magic, but they tend to be shouted down, at best, executed as "traitors to humanity" at worst.
• Moral Myopia: Countless times in the story, people just unilaterally attack Shu with lethal force for no reason, cheering themselves on that killing him will grant them glory, honor, or prestige. When he retaliates, because he doesn't want to die, the attackers twist themselves into a rage yelling "HOW DARE YOU, VILE DEMON!!!!"
• Poor Communication Kills: Subverted. In the early chapters, Shu has the distinct displeasure of being one-sidedly attacked with lethal force because both people and monsters just see him as a mindless beast and he has no way to communicate with them. After he gains the ability to materialize and communicate with people, the monsters appoint him "Demon King" because they operate under Asskicking Equals Authority and he's much, much stronger than them by that point. The humans, on the other hand, immediately go murder crazy the instant they realize he's a "spirit," leaving him no choice but to kill them in self-defense, aside from the unarmed civilians who can't use magic, and those he spares.
• Prophecy Twist: An oracle among the top echelons of the church of El Magio receives a divine prophecy, that comes across in purely symbolic ways, as written "A wicked star shines in the south. Healing greenery spreads out below it. There are two gates: one is orderly wooden door, one is flesh and blood door of resentment. A man can pass through either gate. The day of choice is near." A similar prophecy was stated when a Demon King came about in a distant empire's capital, so all the top brass went full-tilt Do Unto Others Before They Do Unto Us on Shu, to kill him before he became the next "Demon King." In the process, they sent a contingent of Holy Knights that found, and raided, his home village, Iris there as support. She pleaded with the knights to stay their hand when she realized Shu was the "Demon King" she was sent to subjugate, only for the knights to condemn and torture her, causing Shu to retaliate. She then pleads with Shu to stay his hand when he retaliated, going back to her home village to warn the kingdom not to provoke Shu further. Her warnings were ignored. She was unilaterally condemned as a traitor to humanity, and sentenced to be executed as a witch, by being burned at the stake. When Shu learned of this, he went on a Roaring Rampage of Rescue and declared war upon the kingdom of Ramza. It is only then that the top brass, including the royal family, realized that they chose the "flesh and blood door of resentment" and their kingdom is doomed.
• Villain Has a Point: While The Church of Demonism, worshipping the god El Magio, is wrong to call the "monster" or "demon" races inherently, unflinchingly evil, those races are inherently dangerous and often in conflict with humans, so it's not a good idea to approach or mingle with them carelessly. Shu himself was attacked by goblins at the start of the story and Iris had to be rescued from a sadistic werewolf and then man-eating plants more than once. This explains why Shu had no issue with Iris choosing to become a Holy Knight, even though her duty would be to hunt "monsters" like himself or his villagers, in addition to human law enforcement. The issue that led to conflict is when a group of knights and mages, even including a gaggle of novices and trainees came at his village that was in the deepest part of the forest, and he personally pulled away from human territory, to kill everything that moved, all while cheering and patting themselves on the back, completely unprovoked. And then have the gall to get enraged and escalate when he retaliates...