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Reincarnated in Mushoku Tensei: Realistically Overpowered (fanfic)

A reader reincarnates in the world of Mushoku Tensei as Seraphim Greyrat, the first son of Paul and Zenith born instead of Rudeus. Using his meta knowledge to the fullest, he aims to become the strongest existence of that world, using both sword and magic. ... Warning: A SLOW PACE FANF-FIC WITH A LARGE FOCUS ON MAGIC STUDY AND WITH A HIGH LEVEL OF DETAIL. STARTS OFF SIMILAR TO CANON. Seraphim studies the magic system of the world and Battle Aura techniques in depth to understand them fully and gain the best possible advantages. He becomes overpowered without external cheats, a result of his hard work and brains. Note: How this fanfiction is different from others in that many Mushoku Tensei fanfics seem to often get the magic system of the world wrong. The abilities that the Protagonists develop often go against the magic system of the world, are illogical and ridiculous, and something like this in my opinion completely breaks immersion. For example, ridiculous new magic spells and OP sword moves that get invented by an infant MC despite the fact that they are completely devoid of logic and are just impossible without cheats. Here, my Protagonist faces various obstacles and problems during training, that he should, while also gaining insights and does what is realistically possible to take his training and fighting methods to another level. He also achieves things that seem nearly impossible or fantastical, but with good logic and reason behind them. -It is a harem story, but I aim for meaningful romance and deep relationships. It is a harem story. However, harem is not the major focus of the story at all. It only means that the MC will have more than one partner EVENTUALLY. -Because the Protagonist accomplishes A LOT during his early years, there might be no real romance or even harem content anyway for something like 100 chapters. There will be no child sex here as well. There might be some romancing and teasing, but just that, nothing sexual. How this story is different from the original is that it is not about an MC searching for a cure for his ED, being passive and pathetic pervert all throughout the story while screwing around and doing nothing most of the time, but is a man on a mission. Seraphim starts from a similar point as Rudeus, but his actions cause a slowly spreading butterfly effect as he's focused on the most optimal path and BENEFITS. In contrast to Rudeus's perversion, the MC can sometimes instead be amoral and do evil pragmatic things for the sake of his ambitions and loved ones, so people with fragile hearts be warned. He is not as disgusting, but it doesn't mean he's a goody-two-shoe white knight. ... SUMMARY: -MC is born instead of Rudeus with just his meta knowledge and high talent. Taking more after Zenith, he has blonde hair and blue eyes. He trains his mana from an extremely young age, masters Battle Aura and chantless healing magic | A genius of magic and the sword, a determined true main character pursuing supremacy and eternal life. -The story will have a deep dive into the magic system and how the MC interprets it (how I interpret what we know using logic). It might be boring for some people, but it can be very interesting for others (would be for me). -The story starts with the same layout, and has slowly spread out changes as the MC is focused on BENEFITS. -The world is the same as in the original, the only AU change is the MC's body, looks and name.

Jaed21 · Anime & Comics
Not enough ratings
46 Chs

Chapter 20. A letter from Roa and a duel with a Sword King

When I came back home, I learned that Mrs. Eto came over again and made a commotion because her Somal kid had gotten sick due to me drenching him in cold water for the second time.

Paul gave her some customary words and afterwards asked me for an explanation.

I described to him step by step what kind of sight greeted me when I got up the hill to meet with Sylphy.

-I said, because dad told Somal's mom that I won't overuse my magic again, the village's kids ganged up on me and Sylphy for revenge, gathering seven of them. When I got to our meeting place, I saw Sylphy in tears and slightly bleeding from her lip while the statue I built was being hit by rocks. In the end, I threw some cold water at them and scolded them.

As I observed Paul's face while describing things, I felt as if he himself wanted to go and beat up those brats.

Naturally, he gave me a mild warning, but didn't punish me.

After that incident, the village's kids didn't dare to bother either me or Sylphy.

The hill near the large tree became our territory.

In the following few days I continued meeting Sylphy to teach her magic.

Starting from the second day, apart from magic training, I also began training her physically and in the basics of swordsmanship.

She listened obediently and enthusiastically did any exercises and drills I told her, even if they were a bit hard.

Whether she was like this because she respected me, wanted to keep playing with me or wanted to become strong to not be bullied, I motivated her on top of that in various ways and treated our training as 'playing' to make it fun for her.

Even though doing squats, running around the large tree and swinging a stick was tiring, she did not lack spirit and was especially happy when I praised her for her hard work.

Unrelated to that, after two days Paul approached me with a suspicious smile.

"Seraph, are you having fun playing with Sylphy?" He asked me.

"Yeah…"

"That's good. By the way, I asked around in search of a good sparring partner for you and I found someone."

"Hm?" I raised my eyebrows.

Is it the person I hoped it was?

If Paul had sent a letter to Philip, like I thought he would, then it is very possible. In these parts he shouldn't have any other meaningful connections, after all.

"It's my cousin's, Philip's, daughter - young miss of the Boreas family in Roa," Paul said with a grin.

As I thought!

The young miss of the Boreas family, in other words - Eris Boreas Greyrat.

Paul continued with a suspicious smile, "She's 2 years older than you, but since she's a girl, it should be fine. Philip said that she's quite strong and talented for a girl."

"I see…"

"What's with this dull reaction? Aren't you excited to meet up with a cute noble girl?"

"Uh, well I am excited, but…"

But yeah, I simply had a thoughtful reaction.

Probably because the only thought on my mind was - just as I planned.

There was no surprise.

After what I said, Paul had sent a letter to Philip.

I'm pretty sure that Paul had bragged about me quite a lot in the letter.

But regardless of what was written in the letter, after reading all this, Philip should have thought it would be interesting to have me visit Roa and meet Eris, whether just to meet me and scout me out, or hoping it might have some kind of effect on Eris.

I should probably be sent to Roa for a short time, right?

It wouldn't be the other way around?

As if to answer my questions, Paul continued, "Well, anyway, Philip proposed that you would visit Roa for a month. What do you think?"

"I think… it would be interesting," I answered again rather calmly.

Well, I was happy and excited inwardly.

For me, the benefits of visiting Roa 2 years earlier were endless.

It was just that it was all within my expectations - a 1 week to 1 month visit to Roa; something like holidays.

"Then what about Sylphy? Are you fine with leaving her alone?" Paul stared at me with a meaningful look.

I rolled my eyes and answered expressionlessly, "I am not, so can you wait with it for a few more days? I want to teach her some more magic."

I planned to spend around 1 week with Sylphy to build a stronger bond with her first.

That would also be enough to have her learn enough magic and physical exercises, so that I could leave her with homework and she could keep progressing by herself while I'm gone.

"You're teaching Sylphy magic?" Paul asked with a surprised look.

"Yes, she's very talented. I taught her silent casting." I nodded.

"You... Are you serious? You taught her silent spellcasting?"

"Yep. She's talented."

Paul stared at me as if I had grown a second head.

After he came to terms with it, he then told me a little about the person that I was supposed to spar with.

He said that 'she's said to be a little feisty, but I'm sure you'll do just fine' while chuckling.

He didn't tell me more than that, seemingly on purpose, but I already knew.

I knew about the violent and bratty tsundere Eris.

Originally Rudeus only met her about 2 years later as he was forcefully sent off to be Eris's home tutor.

But I felt it would be a waste to just wait for things to happen. Now that Roxy set out on her journey, I also wanted to quickly check something in Roa.

In the next few days I continued to train Sylphy in magic, swordsmanship and physical exercises.

I also began some father and son training with Paul in our home's gym.

It was a bit of a pain doing training with Paul, since he joked too often and didn't take it seriously, but well, I had no reason to refuse him.

I was honestly a bit curious if my bodybuilding methods might help someone like him reach another level as a warrior. Because Battle Aura was said to be all about training the body and sword practice was just a training method, I felt it should.

After one day Paul informed me that the carriage from his cousin's family would visit on the next day, I told Sylphy that I will be going away for a month.

When I told her about it, she begged me to stay and cried.

"N-no!!! Don't go!... Please, don't go. Aaaaawahaa!…"

She looked heartbroken.

I was her only friend.

Without me she would be by herself and have no one to play with.

Maybe she also worried she'd become bullied again.

I gave her a consoling smile while placing a hand on her shoulder and said, "It's okay. You can now use magic, so no one will bully you. I won't be gone forever. I will be back in one month."

That day I brought Sylphy back to the Greyrat house for the first time.

She was very reluctant to come, but not enough to resist me.

I introduced her to Zenith and Lilia. I then instructed both of them to help Sylphy learn the magic Incantations from the Magic Guidebook in my stead.

While being at it, I also asked Paul to teach Sylphy some swordsmanship. He agreed before realizing what he had gotten into.

Well, during this time Sylphy has already learned about half of the Elementary-ranked spells under me and could cast most of them silently. She was a genius.

The only thing that limited her from learning more was her mana and time.

All this wasn't necessary.

But my purpose was for Sylphy to grow closer to our family while I'm gone, like an external member. Then everyone here might also invest themselves into helping Sylphy learn things like reading while I'm away in the future.

Next day was the time of my departure.

I would normally be out playing with Sylphy near the large tree after my morning training, but that day she came over instead to see me off and play at my house.

She also did her final attempt at trying to convince me to stay.

I was forced to use kind words and reason again to make her realize that it wasn't the end of the world and I'll be back soon enough.

To raise her spirits, I promised her that I'll buy her a souvenir when I'm in Roa.

She looked very interested when I mentioned it.

Shortly after noon that day, a carriage appeared at our house's gate.

The doors of the carriage creaked opened and *she* slowly came out.

The *she* was a muscular dark brown-skinned beast woman with a sharp face, a cat's ears, a tiger's tail and a sword at her hip.

"Aah?!"

When the beastwoman looked at us, Sylphy let out a cry and hid behind me.

I swallowed a bit of saliva, then stepped out. Placing a hand on my heart and slightly bowing, I said, "My name is Seraphim Greyrat. Are you Father's old companion, Ghislaine?"

Paul did already tell me that Ghislaine will be picking me up, so I didn't have to act as if I knew absolutely nothing about her.

"Yeah. Sword King Ghislaine," she replied expressionlessly. "You are Paul's son? You're awfully polite. I see you took more after Zenith."

I smiled slightly. "Is that so?"

"Yeah. You look just like her too."

Ghislaine's expression did not change much as she was observing me, probably together with Sylphy.

I said, "Um, Ghislaine-san, can I duel you?"

"Hm?" Ghislaine looked surprised.

"I'm a magician. I would like to see if my moves will work on a Sword King."

A chance to duel a Sword King, without too many prying eyes.

I wonder just how well my magic would fare.

For Paul, he was defenseless against my Gravity Magic; if affected, he could only throw his sword at me.

But what about a completely different existence - a Sword King?

Besides, this kind of thing might be a quick ticket toward gaining Ghislaine's respect.

"So that's it. Well, that's fine. And Ghislaine is enough."

Ghislaine agreed easily.

Judging by her expressions, she probably did not expect much from me. I wonder how much she knew about me from Paul and Philip?

Eitherway, I said that just in case: "I apologize in advance if I hurt you. I'll try to be careful. And if you do get hurt, I can quickly use healing magic."

"That's fine. Don't worry about it."

"Well then." I put aside the wooden sword that I used to 'play' with Sylphy. I then stepped out and faced Ghislaine with just my two open hands.

Ghislaine looked back at my expressionlessly, her hand casually resting on the pommel of her sword.

"Well then, let's start."

I slightly stretched out both my hands.

And I used Gravity Magic with my right hand.

The simplest and the most efficient use of Gravity Magic - Zero Gravity Field.

In an area of effect, it removes all effects of Gravity, making people and things float about like on a spaceship.

"Hm?!" As a result, Ghislaine showed a surprised expression as she suddenly started floating, her limbs and tail flailing around as her body's balance became distorted.

At the same time I started casting a spell with my left hand - Intermediate Rank Stone Cannon.

I practiced with this spell a lot. It was my fastest spell.

The fastest when it came to the projectile's flying speed, that is.

I created a slim and long cone-shaped bullet, hardened it, then added an accelerating spin to it.

I then packed my hand and bullet full of mana, making my attack ready for launch.

The entire process took about 2 seconds. This was as much as I needed to create my full-power stone cannon at my current level.

By now Ghislaine had already regained most of her balance. She still looked surprised as she floated in mid-air, failing to touch the ground to gain a strong position, but she already drew her sword and was ready to swing it while afloat.

She also attempted to cut the 'magic' around her, but it failed.

Honestly, she looked surprisingly level-headed for her situation. Perhaps that was the result of her belief in her strength.

I exchanged silent glances with Ghislaine. I think she would get the message to brace herself.

Then I launched my stone cannon.

'Ghislaine, if it pierces your stomach, sorry. I'll heal you quickly. I know you're tough, you'll be fine!' I thought.

But it was necessary for me to test the limits of my strength.

As I shot out my slim bullet, Ghislaine's sword moved.

Chang!

When Ghislaine stopped her movement with her sword arm out-stretched, I saw that she was uninjured.

Meanwhile my bullet… could not be found anywhere.

One might think that after being cut down, the two halves should have floated in the zero gravity area, but it was simply not there.

The mana that formed it disintegrated.

It was the result of an Advanced-rank technique of the Water God style that allows a swordsman to cut down magic spells.

Although Ghislaine was a Sword King of the Sword God Style, knowing a technique to counter magic was still a must for all decent swordsmen.

"So it failed," I murmured.

I carefully looked at Ghislaine.

She was sending me a shocked look. Her eyes were widened and a bit of sweat was building up on her head as she continued waving around her hands and feet in a mild panic.

I see.

I asked, "Ghislaine, can you free yourself and drop down?"

Ghislaine frowned. Her posture relaxing, she took her eyepatch, then started swinging her sword around herself.

But once again, what she was doing was ineffective.

Ghislaine continued floating in the air, unable to advance or retreat, and only capable of moving her limbs.

"No…"

She couldn't free herself.

I see.

As I thought, Gravity Magic really ignores Battle Aura.

Even a Sword King can't resist it!

It does not matter how strong or fast your body is, if you lose everything that keeps you grounded to the earth, you will begin to float in mid-air and be mostly helpless.

It was that kind of logic.

This was the power of Gravity Magic, the power of physics.

And a counter against all Battle Aura users.

Though there should still be ways to go around it.

If Ghislaine threw her sword at me, I would probably not be able to avoid it.

If she caused a shockwave with a sword swing, there was a chance she would be pushed back out of my magic's range.

But the fact was that she was unable to approach me on foot even if I just used Gravity Magic in its simplest form.

At the beginning, her balance was interrupted as well, but unfortunately my spell casting was too slow to make good use of it.

As for my Stone Cannon…

Perhaps I subconsciously held back a little, since it was Ghislaine, but that attack should still be about 90% of my power.

Not quite enough yet to get through a real Sword King, it seemed…

If I used Ice Magic instead, I could have frozen and killed Ghislaine most likely. I already tried it on Paul - Water and Ice Magic combined with simple Gravity Magic was an astute move that's difficult to counter.

If I used Fire Magic, I could have fried her and she would have no choice but to retreat.

But I was still not at the level where my stone cannon could one-shot a semi-immobilized Sword King.

A shame.

Well, I'm still 5 years old, so there's plenty of room for me to improve.

"How was that? My kid is quite a genius with magic, haha!" Paul walked out of the house at that moment with a grin.

"Ghislaine, it's been a while." Zenith also walked out, with a gentle smile.

"Hm." Ghislaine let out a low grunt.

I canceled my Gravity Magic and she dropped to the ground, landing on all fours like a cat.

Ghislaine ignored Zenith and Paul after straightening her and looked at me with a surprised face. "What was it that you used? I never saw magic like this."

"It's my personal magic." I smiled slightly.

"...I see."

"What do you think? When Seraph uses this move, even with Advanced rank in Water God Style, I can't go out. Was it the same with you?" Paul asked.

"Hn. I couldn't move. I could move around and swing my sword, but it felt as if I'm not going anywhere," Ghislaine replied with a solemn look.

"I know, right? I can't cut it down too. This spell is a counter against the Sword God Style. My son is a real genius! Haha!"

I smiled a little.

When I first used Gravity Magic against Paul, he was indignant. He was not willing to accept that he was completely done in by a single spell.

Quite a transformation. Now he was bragging about me.

But I felt it's normal.

If I spent my entire life training with the sword, adventuring and slaying countless monsters, just to be immobilized by a toddler dabbling in magic, I would also want to deny reality.

"..." Toward Paul's bragging, Ghislaine was silent.

"Ghislaine, I'm glad to see you doing well. You'll be taking our boy to Roa, right?" Zenith spoke up as she approached us with Paul.

At those words, Ghislaine's expression slightly relaxed and she nodded. "That's right."

Following that, Ghislaine began chatting with Paul and Zenith.

In the meantime I turned to Sylphy who was still staring with mouth agape and an apprehensive expression.

"Sylphy, I'll be leaving."

"Mm-mh…"

Sylphy looked depressed and tears formed in her eyes, but I feel she was forced to realize by now that I would leave no matter what.

"You'll keep practicing magic and doing what I told you?" I asked her.

Before leaving I gave Sylphy homework - I told her to exhaust her mana every day and gave her a workout plan to follow while I'm gone.

In addition, I instructed her on a practice method to do at home that might help her grasp pure mana manipulation - if she manages that, I would teach her Disrupt Magic.

Once Sylphy learns Disrupt Magic, I could also begin improving my ability to resist magical interrupts from people like Orsted. The younger I am when I start this, the better it would probably be for me.

"Yes," Sylphy said.

"Good. When I come back, I'll test you and we'll play."

After that I picked up my hand-luggage from inside the house that included my notebooks.

Paul brought in some more luggage from the inside, then told me, "As you saw, that woman is a Sword King. When it comes to the blade, you won't find a better teacher this side of the country apart from the Sword Sanctum. If you train with her, you'll improve much better than with me. Don't waste this chance."

"Yes." I nodded.

"Seraph!" After that, a concerned Zenith approached me to see me off with tears in her eyes.

I then boarded the carriage with Ghislaine.

As I waved at everyone through the open window, the carriage eventually set off.

Sylphy was also waving her hand in a farewell, crying. 

Nearby, Zenith was also crying in Paul's arms. "My only son is leaving me for a whole month. I'll be so lonely!"

"No worries. I'll take care of that loneliness."

As the house was no longer visible from within the carriage, Ghislaine spoke up, "Your parents really love you, don't they?"

"...Yeah."

My and Ghislaine sat opposite each other, each observing the other silently.

I could feel that my magic left a profound impression on Ghislaine.

On that matter, I spoke up, "Was my magic so easy to cut down?"

"Hm? You mean the spell that you shot at me when I was in mid-air?"

"Yes."

Ghislaine shook her head. "No. I had a hard time deflecting it. It was very fast."

"I see. Not quite fast enough for a Sword King."

Ghislaine didn't reply. No more commentary.

Maybe she thought: 'Just who do you think a Sword King is?'

After that, she did not speak up on her own either. Not much of a talker.

But well, if she says that my stone cannon was difficult to cut down, I would be satisfied.

Did this mean that after another year or so of magic training, she won't be able to deflect it?

Well, I look forward to the future.

Even Rudeus always had incredibly strong magic as a kid. Except that he never brought it out and didn't do any specialized combat training directed at destructive power before he turned 10 and ended up on the Demon Continent.

But at around 10 years of age his mana pool already ended its growth stage.

If apart from getting a planet-sized mana pool and making dolls, I focused most of my childhood on becoming a killing machine, just how strong could I become?

While doing some magic training and making small talk with Ghislaine for the next few hours, the carriage eventually reached Roa - the largest city of the Fitoa region.

Leaving the rural village, I was to spend a month in the Boreas estate.

A new world of opportunities was open before me.

I was excited.