Haruyoshi Kugano believed he was one of the strongest Onmyōdō of all time. And he used this strength to protect the people of Japan... but his quest for power eventually lead to those who he trusted betraying him and his students, ending his life. Before his demise, however, he cast one final spell, one which would allow him to be reborn elsewhere...
...with success, as he is reincarnated as Seika Lamprogue, the third son of the Lamprogue clan. After ruminating on the mistakes of his past life, Seika seeks an average life in a world of swords and sorcery, in which he can focus on his own happiness, even at the cost of the strong.
This novel provides examples of:
- Allegorical Character: In-Universe. Before their death, Seika's master in Onmyodo wrote a poem about a man who was actually a monster, who they still felt fine around, representing how they had become unstable as they grew older but could still find love for the moon. Seika in turn composed a poem about how he had hated his master but found life lacking now that he was gone. He then murdered his master before he could hear their reaction, and declared that the monster in his master's poem represented himself.The Master's Poem: "On a night when the moon is almost hauntingly beautiful, I meet someone. Even if that person is a monster, not a man, for some reason, I feel fine."
Seika's Poem: "A cloudless night sky seems lacking, somehow. Maybe I hated you, because you were like clouds covering the moon, but now that you're gone, that's how I feel." - Alone with the Psycho: Repeatedly, whenever Seika is alone with an enemy. Because this is Seika, however, he's the psycho in those situations.
- Appeal to Tradition: Gyu attempts to argue against Seika going to the Academy City Londonea by stating that two sons of the Lamprouge family have never followed the same path - the oldest son becomes the next lord, the second son learns magic, and the third son joins the army. This backfires when their father agrees - and states that Gyu will be joining the army instead of Seika.
- Big Brother Bully: Gyu Lamprouge, one of Seika's older brothers. After learning that Seika has no magical talent, he repeatedly harasses him over it.
- Big Brother Instinct: Unlike Gyu, Luft Lamprouge, Seika's oldest brother, is a Nice Guy and tries to protect both his brothers from mistreatment, shielding Seika from Gyu's bullying and asking Seika to go easy on Gyu during their Wizard Duel.
- Blood Knight: Amyu gets really excited during battles, to the point that when her adventuring group was decimated in a vicious battle, her only response was to get starry-eyed and request another adventure.
- Character Development: After Gyu returns to the story when Seika returns home, he's a lot more mature and responsible due to taking to the army and a more physically active role much better than studying magic. It's assisted by his responsibility to protect the Holy Princess, whose flighty nature forces him to be The Reliable One. It's strengthened even further by the finale, as Gly and the Holy Princess end up aiding Seika in freeing Amyu from prison.
- Chekhov's Gun:
- The fight against the demon assassin establishes that Seika can bring himself back from the dead, and the end of his fight against Kyle shows that he can extend that ability to others. In the finale, Seika undoes his Roaring Rampage of Revenge against the capital by bringing everyone who died in the attack back to life.
- When Seika and Amyu first become friends, Seika mentions that he'd like to go adventuring with Amyu again eventually, and they reaffirm this promise when they visit Seika's family home. In the finale, after Seika and Amyu are expelled from Londonea to prevent war from breaking out over their status as the Demon King and the Hero, they wind up traveling around together, with Yifa and Mabel later joining them.
- Combat Pragmatist: Gyu defeated Amyu in their magic-less duel by faking an incantation.
- Covert Pervert: Amyu enjoys two things: fighting, and talking about sex. It's enough that Seika thinks she sounds like an old man when she asks if he ever got up to anything with Yifa.
- Creepy Child: Seika leans into this on occasion, particularly when confronting an enemy alone.
- Death by Irony: Seika is killed when the Imperial government sends his favorite student to kill him. He later reveals that he was also a Bastard Understudy who killed his master.
- Death Is Cheap: For Seika, at least, as he's able to prepare spells to bring him back from the dead. Averted for Kyle, as while Seika could bring him back from the dead (and fully intended to at first), he's talked down from it as the magic required to bring Kyle back would certainly reveal his true power to the world.
- Evolving Credits: After the Tournament Arc and Mabel going back to her actual hair color, Mabel is shown in the opening, with her integrated into group shots in both the opening and ending.
- Fake Ultimate Hero: Mabel Crane's purpose. She's the same age and gender as Amyu, and dyes her own hair so she shares the same hair color as her, while also being named after the second Hero. She was enrolled into the academy a year late to make it look like her identity was being hidden, and she was trained to be an incredibly proficient fighter. All of this was in preparation for the tournament, where she was intended to be killed by Kyle in the final round, making the demons believe that the Hero had been killed... all while Amyu, the real Hero, slides under the radar. It would have gone according to plan had Seika not intervened; as a direct result, Mabel survived and Kyle ended up getting killed.
- False Flag Operation: Seika has one of his summons stir up an Elder Newt and cause it to go on a rampage towards the Lamprouge manor so that he has an excuse to defeat it publically and supplant Gyu as the one to be educated in magic.
- Formula with a Twist: The light novel follows the typical "person from Japan dies and gets reincarnated in a world full of European Fantasy Tropes", but with a couple of twists:
- The main character died during the feudal era in Japan, rather than the modern era.
- The main character retains his spiritual power and follows a separate system than most of the population in the new world who utilize a more traditional magic-based system, resulting in the kinds of hurdles most other protagonists of this type typically don't deal with.
- Four-Temperament Ensemble: The main cast acts as this, with Yifa as the kind and sociable Sanguine, Amyu as the energetic and impulsive Choleric, Mabel as the quiet and moody Melancholic, and Seika as the laid-back and calm Phlegmatic.
- Heroic Bastard: Seika is the child of Lord Lamprouge and a mistress, resulting in him being shunned until he defeats the Elder Newt. Lord Lamprouge later muses that Seika is mostly likely really the result of his brother Gilbert and a demon woman, making Seika his nephew, rather than his son.
- Leave No Witnesses: Seika's usual policy for those who see his true strength. Gly survives the encounter because Seika promised Luft to spare him, but once the two assassins sent after Amyu learn of Seika's abilities and knowledge, their lives are forfeit.
- The Man Behind the Man: Seika seeks to become this in his second life, and befriends Amyu in order to make her into the World's Strongest Woman.
- Manipulative Bastard: In his original life, Seika was killed when his government turned against him for being too powerful. Because of his desire to avoid tragedy, he decides that in his second life, he'll be cunning.
- Mass Resurrection: After the Holy Princess and Gly help Seika break Amyu out of prison, he performs this to undo the damage caused by his Roaring Rampage of Revenge in the capital.
- Mind Probe: Seika interrogates a spy for the demons by summoning an ayakashi capable of reading minds and repeating what the person is thinking. It turns downright nightmarish when the ayakashi's payment is rendered - eating the spy alive, all while cackling his final terrified thoughts out loud.
- Never Be Hurt Again: The reason why Seika sought to become the strongest in his first life, as he believed that it would prevent him from losing anything he cared about. Unfortunately, the Imperial government considered him Too Powerful to Live, and used his beloved students as hostages, even sending his favorite former student to kill him.
- No Challenge Equals No Satisfaction: Amyu's intent when attending Londonea is to become strong enough that fighting anyone just becomes boring so that she can remove her Blood Knight tendencies and be a normal person.
- The Perils of Being the Best: Seika already faced the perils of being the World's Strongest Man in his first life, which ended in him being betrayed by the Imperial Government due to their fear and jealousy of him, with them taking his students hostage and sending his most beloved former student to kill him. His goal in his second life is to be cunning instead of strong, acting as The Man Behind the Man for Amyu and fulfilling his goals through subterfuge and trickery rather than sheer power. Unfortunately, he's destined to become the Demon King, which causes some issues with him being the best friend of The Hero.
- Prince Charmless: The blond prince shown in episode 9 acts like he can gain anything he want with his wealth, even his elven advisor supports his wretched schemes and even tries to convince Yifa that his so-called "harem" is a group of girls that are learning to be important members in high society, but when he shows his true colors and Seika just can't stand the prince's arrogance, he flat-out tells him that he's nothing more than a self-centered jerk that doesn't even deserve his so-called "prince" title since he doesn't even care about the "people" whom he is supposed to protect in his little kingdom and only cares about what he really wants to do with his little "harem".
- Reincarnate in Another World: Seika died in our world and kept his exorcist powers when going to the new world.
- Roaring Rampage of Revenge: After the Holy Kingdom arrests Amyu on false charges in order to execute her and prevent a war from breaking out with demons, Seika flies to the capital to forcefully break her own, using his Technicolor Fire and a Kamaitachi to burn and cut through everyone in his way.
- Running Gag: Seika gets motion sick whenever he needs to take a carriage.
- Satellite Character: Seika's kudagitsune ayakashi, who spends most of her time hiding in his hair in her fox form. She never appears around other characters to keep Seika's status a secret, with her main purpose being to ask Seika questions so that the audience can understand his actions more.
- Secret Secret-Keeper: Lord Lamprouge knows that Seika doesn't use traditional magic and is aware of the suspiciousness behind the Elder Newt affair, but sends him to Londonea anyway. It's because Seika is actually Lord Lamprouge's nephew, most likely a Human-Demon Hybrid, and can become either the Big Good or the Big Bad, with him knowing that Londonea is a good place that will hopefully make him a hero.
- There Is Only One Bed: In episode 8, while staying at Astelia, Prince Cecilio summons Yifa to his room at night, but she refuses and goes to Seika's room. They have to share the bed because Yifa doesn't want Seika to sleep on the floor.
- Took a Level in Badass: Joining the army has really done wonders for Gyu's competence to the point that he could even defeat Amyu in a spar.
- Took a Level in Kindness: Gyu is much more civil with Seika when they meet again at the Lamprouge house for the first time since going separate ways (army and the wizard school).
- Tournament Arc: The plot of volume 3 starts with the academy's principal asking Seika to participate in a combat tournament in Capital City, along with new student Mabel Crane.
- Weaksauce Weakness: Seika - the World's Strongest Man - gets extreme motion sickness on land vehicles, to the point where he needs to lie down after taking a carriage anywhere. He could avoid it in his past life since he could just fly around on a dragon wherever he needed to go, but his desire to lay low forces him onto them quite often. It's mostly Played for Laughs at Seika's expense.
- Wizard Duel: After Seika defeats an Elder Newt and gets his father's permission to enter the world's Wizarding School, Gly challenges him to a duel for the right to attend the school - if Gly loses, he follows their father's commands and joins the army to uphold tradition, and if Seika loses, he's forced to leave the Lamprouge house immediately.
- Wizarding School: Academy City Londonea is a magic school where several of the country Court Mage learned.
- World's Strongest Man: As per the title, Seika was the strongest exorcist in his original life, and kept that strength when reincarnated.
- Wrong Context Magic: Seika is unable to use normal magic that others in his new world use, but he does have exorcism magic, which operates somewhat differently.
- You Remind Me of X: While Seika never actually says it, he notes that Amyu and the Holy Princess remind him of two people from his past life; Amyu is the spitting image of his student who watched him die, and the Holy Princess's personality reminds him of his wife. It's Amyu's resemblance to his student that leads to him going on a Roaring Rampage of Revenge when the Holy Kingdom arrests her with the intent to "disappear" her.
