Time to go to a gym with my ghost trainer
"I have a grudge against your father. Therefore... Do I grant you more power than your father?"
— Tre'ainar, The Great Demon King, offering his guidance towards our MC, Earth
''Breakthrough with the Forbidden Master – So what if the Hero’s son is the Demon King’s disciple~'' (禁断師弟でブレイクスルー～勇者の息子が魔王の弟子で何が悪い～, Kindan Shitei de Breakthrough ~ Yuusha no Musuko ga Maou no Deshi de Nani ga Warui ~ in the original Japanese) is a Japanese Light Novel series written by Brother Aneki (アニッキーブラッザー) with its web novel first published in Shōsetsuka ni Narō at 2019/05/15.
“Compared to our time, the current generation just aren’t as reliable” they said, “Still, isn’t he the son of the Hero?” How annoying.
It’s been over ten years since the battle between mankind and the demons ended. The children of the heroes who saved the world are all grown up. One of them, Earth, was the son of the hero himself, and everyone expected him to succeed his father as a warrior and defend his country.
... Unfortunately, reality can often be cruel. Not only did Earth have no talent for the sword whatsoever, only managing to keep up with sheer hard work, but His friends quickly surpassed him as prodigies, and he because of his pedigree, no one, not even his parents (who are rarely if ever around) expect anything of him. This, combined with his childhood friend (the literal princess of the country) constantly forcing him to train and making him look worse around his fellow students (particularly the girls), Earth was always wary of his father’s title, seeing it as a burden more than anything else.
One day, however, Earth is shocked to find his father’s sword, which was used to overthrow the Demon King, sealed in his family’s mansion. And with it, the ghost of the Great Demon King who was unable to pass on and continued to roam the world.
Being the only one who could see the former Demon King, he came to possess the young man. Watching his daily struggles and frustration regarding his situation, one day the former demonic emperor whispers to Earth on a whim:
“I have a grudge against your father. If you want to get back at your father and the world, I’ll train you. I’m free.”
Earth receives special personal guidance from the Demon King just to get back at his parents and the world. Then, in the coming days, the hero’s parents, the heroes of the past, the first love, the princess childhood friend, the geniuses of the era, and the world will tremble.
As there are multiple iteration of the series: Beware of unmarked spoilers.
The series contains the following tropes:
- Abhorrent Admirer: After Earth beats Shinobu in a game of go, she's enamored with him and tries to convince him to start another match. When she realizes he's a strong opponent, her attraction only skyrockets, much to his chagrin.
- Adaptation Deviation: In the novel, Shinobu is angered by his refusal to finish her off and forces him into finishing the fight, albeit ending with her being defeated and on the ground before she recalls what he said earlier about not wanting to bash in her face because it was too cute. When Earth makes this same statement after he stops his fist just short of hitting her, Shinobu's too flustered by his compliment to goad him into finishing the fight.
- Adults Are Useless: Neither of Earth's parents spends much time and effort raising him. His mother takes it pretty badly when it finally sinks in she knows nothing about her own son, whose upbringing she dumped on their maid. His father isn't any better, having refused to train him (despite Earth having supposed to be his successor), excusing himself as being busy with his job.
- And the Adventure Continues: The manga ends after Earth and Aka's
- Arc Words: "I want to be someone who can see everything in the world!"
- Better Off with the Bad Guys: Everyone in Earth's life, from his parents, his more talented peers, even Sadiz, casually disregarded or dismissed his efforts to try and live up to the expectations he was under. It's not until Tre'ainar starts haunting him that Earth gets the dedicated guidance he needs to make progress, which he does very quickly. During the graduation tournament, when everyone else is interrogating or criticizing Earth for using the Demon King's techniques, Tre'ainar is telling him to reveal Tre'ainar's existence to his father so he can take the heat from the boy. Unsurprisingly, Earth sides with Tre'ainar and leaves his old life behind entirely after Calling the Old Man Out.
- Character Development: Earth starts off the series as being deeply bitter about his shortcomings and being constantly compared to his parents while also failing to meet everyone's expectations. Initially, he's eager to prove to everyone he can live up to those expectations and also step out of his father's shadow, though he later becomes more interested in proving his own beliefs and discarding his old desires to live up to everyone's expectations (which is justified seeing as how everyone's now scared of him). This is reflected early on when he becomes Tre'ainar's student; he initially trains with a sword, but later discards it and focuses on switching to magic-based abilities and fighting with his fists when the demon king tells him he isn't suited to use a sword and should switch his focus elsewhere.
- Challenge Seeker: Shinobu craves nothing more than a great challenge. When Earth beats her in a game of go (with the demon king's assistance), she's amazed and immediately demands a rematch. She's similarly thrilled when she learns Earth is a Worthy Opponent. Her backstory goes into more detail, showing that she became incredibly bored with school and low-ranking assignments because they were too easy, leaving Japon with her brother to become hunters.
- Chick Magnet: Heavily deconstructed. Jose has all the trappings of a Stock Light-Novel Hero in that he's incredibly powerful, is engaged to the princess of his country, and has his own harem. The problem is that his harem is so enamored with him that they take any criticism against Jose personally and get incredibly violent, which only feeds Jose's ego. It's later shown that Jose doesn't actually reciprocate their feelings despite his promises to marry them, feeling that he is deserving of their love and attention because he's strong. Once again, it bears repeating that Jose is engaged but makes an (empty) promise to marry his harem anyway.
- Dark Is Not Evil: The Demon King Tre'ainar. While he did eventually become a dark warlord who willingly destroyed much of human civilization while uniting demonkind under him, he started out as one of many ordinary demons who merely wanted to leave the Underworld and acquire happier lives for their loved ones and themselves, and even originally desired to create peace and equality between demons and humans with the help of Earth’s father. Sadly, however, he became embittered and lost hope for achieving the goal of equality between humans and demons as he saw the endless cruelty and prejudice of humanity towards his kind simply for being different than them. Even after he became so bitter, he still prevented a horrific calamity that would have destroyed an entire continent from happening, and permanently destroyed the knowledge of how to make a weapon like that to ensure the world’s safety instead of using it himself for more power.
- Defector from Decadence: Aka reveals in a letter to Earth that he was actually part of the demon king's army, but left when he could no longer stomach the wanton violence and cruelty of his fellows and parents.
- Doesn't Know Their Own Child: Once Earth runs away, his parents are forced to accept the painful realization that they understand and know almost nothing about their son. To the point that they actually realize that Earth is justified when he decided to leave and run away.
- Good Cannot Comprehend Evil: In Volume 3, a group of shinobi attack Aka under the belief he's an evil ogre who needs to be put down. They initially don't understand why Earth goes to great lengths to protect him and stop Aka's rampage at the cost of his physical health, not until the fighting ends and they realize their mistakes. They offer to fix the damages, but Aka, still bitter they attacked him, tells them to leave but agrees to let Shinobu tend to Earth's wounds.
- Hard Work Hardly Works: While Earth is a genuinely good fighter, he earned his merits through his dedication to training. The problem is that he's unfavorably compared to his childhood friends, all of whom are shown to be prodigies who learn much faster than he could. It isn't until he meets Tre'ainar and the latter agrees to train him that he learns part of his problem is that, as Tre'ainar points out, he doesn't have any real talent in regards to being a Magic Swordsman and he needs to change his fighting style.
- Hates Their Parent: Downplayed. Earth doesn't hate his parents despite their neglect, but constantly being compared to them and being found lacking has made him wish he wasn't their son.
- Heroic BSoD: As Earth finds out the hard way at the tournament, using one of the signature demon king techniques in front of the heroes that killed him and even his own maid, who lost her family to said technique, does not end well as everyone flips the everliving hell out.
- Humans Are Bastards: The reason for the war happening at all is because humanity's Fantastic Racism towards demons escalated to the point where Tre'ainar realized co-existence was flat-out impossible. A theme in the series is Earth witnessing this for himself; while he does meet genuinely good humans who come to learn that not all demons or monsters are inherently bad, he meets several humans who are the absolute scum of the Earth.
- Innocently Insensitive: By no exaggeration, just about EVERYONE in the capital is this with Earth. His friends, parents, maid, class teachers, fellow students, citizens and even the guards. Just about everyone feels the need to comment how Earth isn't living up to the standards that they placed him in, or how inferior he is to both his parents and childhood friends. His parents playfully reveal that they have zero belief that he could actually win in the graduation tournament, and his maid Sadiz unintentionally plays and toys with his feelings that everyone believes is simply a Precocious Crush that he'd grow out of.
- It's Not You, It's My Enemies: At the end of Volume 3, Earth offers Aka to join up with him for an adventure. While Aka seemingly agrees to join him at first, he leaves in the middle of the night and explains to Earth in a letter that he can't join Earth on his adventures because of his bloody history with the demon king's army, nor can he bring himself to bring unwanted attention to Earth for being friends with an ogre.
- Light Is Not Good: The Seven Heroes, and humanity as a whole. Outwardly at first, the Seven Heroes and humanity appear to be the so-called "good guys" in the conflict between demons and humans. The reality, which Earth discovers as he travels the world and meets many friends and enemies, is that humans started the human-demon war by being so utterly cruel and racist against demons simply for being different than them that they butchered and murdered countless innocent demons seeking to live peaceful lives on the surface, to the point that demonkind decided to fight back to get revenge.
- Meaningful Name: Earth. His name can also translate to terra, and he’s best with terra-style magic, and relies on using the Earth itself beneath him in order to have proper footwork during fights.
- Overshadowed by Awesome: Few people acknowledge the hard work Earth has put into becoming one of the top students in the academy since he's been held to higher standards than anyone else because of his father. It does not help that he's constantly being compared to his talented childhood friends.
- The Runaway: Towards the end of Volume 1, after the Graduation Tournament goes south and seeing everyone go against him, parents included, Earth finally has enough and decides to leave.
- Screw the Rules, I'm Doing What's Right!: In the aftermath of Earth using one of the demon king's techniques, Phianse's father declares him an outcast and tells Phianse to forget about him. Instead, she gathers her and Earth's childhood friends plus his maid Sadiz as well as his mother and leaves the empire to go look for him.
- Shipper on Deck: Earth's and Phianse fathers, fully convinced that their children are mutually in love (as opposed to one-sided delusion by Phianse), plan to announce their engagement. Their plan is put on hold after Earth runs away from the capital.
- Slave to PR: Phianse's father makes an official declaration that Earth is no longer welcome in the empire and is effectively exiled. While it obviously pains him to do this, especially with how it affects his daughter, he does it so as to placate the masses as they still haven't fully recovered from the horrors of the recent war.
- Surprisingly Realistic Outcome: In the manga, Aka rebukes the ninjas offer to repair his home and fix his crop field and tells them to leave him alone despite their apology. Given how this happens shortly after they came to kill him and destroyed his home, it's natural that even someone as kind-hearted as Aka isn't keen on forgiving his enemies so quickly.
- Trauma Button: Sadiz the maid lost her hometown to an attack by the Demon Armies as a child. The event haunts her even into adulthood, as the memory of it can intrude when she's going about her normal day. She can handle that normally but when, during the academy's graduation tournament, she witnesses her masters' son Earth using the same technique the Demon King used to destroy her home and family, she goes into a panic attack and Earth's father steps in to stop him from proceeding any further. Earth had never intended to harm Sadiz in such a way, and the fact that he did is perhaps the sole thing he regrets about the events of that day, which included Calling the Old Man Out and effectively disowning everyone else in his life.
- Tsundere: Phianse is a model deconstruction of the archetype. She isolates Earth socially from other women out of jealousy while not telling him of her own feelings, and harasses him daily, making it seem as though she hates him. Earth is completely oblivious that her treatment of him is supposed to be expression of love, and not bullying, and genuinely dislikes her heavily for being someone he sees as an abuser.
- We Used to Be Friends: Earth is childhood friends with the children of some of the other Seven Heroes, with Phianse being among them. By the present day, however, they've all drifted apart. Rebal notes how Earth used to be the unofficial leader of the group, but the gap in power between them in later years has more or less erased most of their friendship. It isn't until during the graduation tournament that Rebal state he still does consider him his friend. As if to prove this statement, Phianse gathers their old group plus Sadiz and leaves the empire to go find Earth, royal decree be damned.
- Wowing Cthulhu: There are times that Earth impresses his master, who was the late feared demon king. Example of this when Earth uses a move that he was supposed to do after 6 months of training only for him to do it under 2 months and in the middle of a battle.
