AN: Enjoy the chapter

Ch 8 The Day Before Thirteen

El Dorado

A loud sigh echoes throughout the Castle of El Dorado. The two Knights that stood in the same room looked at their Lord, reading a letter sent by a messenger from Tempest.

"My Lord, is something the matter?" Alrose asked the Platinum Saber, sensing he was displeased.

Leon stood up from his desk and walked over to the door. "Alrose, Claude, I'll be gone for a week." He informed his Subordinates, "You two are in charge until I get back,"

Claude looks over to the blonde Demon Lord, curious about where he was heading. "Lord Cromwell, where are you going?" The Knight asked his Lord.

The Platinum Saber raised the letter he received, showing it to the two. The letter has a wax seal of a certain school. "Seems like that foolish old man has hired additional help to my class this coming year," Leon informed his Subordinates. "An Assistant Professor to help out around the Classroom."

"The school of weak Majins?" Alrose asked, curious why they sent a letter to him.

"Indeed, I have to meet that old coot and this Remus Lupin about Defense's curriculum," Leon added, opening the large doors.

The two Knights followed Leon down the hall, "If you don't mind, Lord Cromwell. Why has the Headmaster asked to speak with Remus Lupin about your class lessons to the students?" Claude asked the Platinum Saber.

Leon eyes his Subordinate, hearing his question. "I have no idea, Claude." The blonde Demi-God answered, "My guess is that this Remus Lupin has a different teaching style than mine. If that's the case, then I have to meet with him to collaborate on the lessons."

"If you're going back to that school, then bring a Subordinate with you-"

"I'll bring a Familiar, I don't want to insight more suspicions on me than I already have," Leon stated, leaving his Subordinate to take care of whatever needed to be done in El Dorado. "Take care of El Dorado while I'm gone."

"Yes, my Lord."

Jura Tempest Federation

It was mid-morning, and Diablo with the Pale Hobgoblin Maids finished preparing breakfast.

Shinsha yawns, hopping down the stairs in her Slime form. "Good morning, Diablo-san." The Daughter of Rimuru greeted her Family's Butler.

Diablo inclines his head to the young mistress, greeting her as she made it to the table. "Good morning, young mistress." The Primordial Demon greeted the young mistress of Tempest. "We have prepared breakfast for you all,"

"Thank you, Diablo-san!" Shinsha smiled, reverting to her Human form, and walked over to the table.

Just one cue, Rimuru, and Veldora came in after getting ready for the day. "Hmm? Now that smells great!" Veldora smiles walking to the table, ready to eat. "Bacon and eggs?"

"Yes, I have the chance to research Harry-sama's World and read many interesting recipes that weren't made in our World," Diablo said with a smile.

"I can confirm that there's a lot of food in that World that I missed," Rimuru commented, thinking of the many foods that he used to enjoy in that World. He then looks around, noticing that someone "Diablo, where is Harry?"

The black-haired Demon looks at his Lord, hearing his question. "If I have to guess, he's probably still asleep in his room, Rimuru-sama," Diablo informed the Demon Lord.

Veldora leans back, "He's still asleep this early in the morning? I guess Hakurou's training has finally gotten to him." The Storm Dragon commented, remembering the Arch Mage was training yesterday.

"Should I get him, Papa?" Shinsha asked her Father, wanting Harry to eat with them.

Rimuru got up from the mat, "Don't worry, I'll get your Brother, Shinsha." The Demon Lord made his way back to the stairs, heading upstairs to his Son's room.

The Demon Lord approached his Son's room, knocking on his door. "Harry? It's breakfast, time to get up." Rimuru called for the Arch Mage through the door. He could hear his Son's groans when he knocked on the door.

"Shut up…" A deep muffled voice spoke behind the door.

Rimuru steps back, hearing a deep voice in his Son's room. "Harry? Are you okay? Are you sick?" The Demon Lord asked his Son, getting a bit concerned. "What is going on?"

{Notice: Today is the individual known as Harry Tempest's th-}

"Not now Ceil," Rimuru opens the door of Harry's room, "Harry, are you okay? Your voice has changed." He stated, coming in uninvited.

Another moan came from the Arch Mage's sleeping body as Rimuru opens the curtains. Harry moans, sitting up from his futon mat. "Shut the blinds, it's too damn bright out."

"Harry, how many-eh? Did your voice change?" Rimuru turns around before jumping at the sight of his Son. "EH!?"

"Geez, Dad stop all that yelling," Harry placed his hand on his head, annoyed that his Father was screaming so early in the morning.

Rimuru was speechless, his Son seemly to have changed overnight. His hair was still the same, but it was darker green than black, and his eyes though his pupils were already yellow there was a hint of red in his iris, his complexion was paler than before, and his nails were black.

'C-Ceil what happen to Harry?' Rimuru asked his Ultimate Skill, unsure what was going on.

{Notice: the individual known as Harry Tempest has gone through puberty.} Ceil informed her master of what had transpired with Harry.

'Puberty? This is not puberty!' Rimuru mentally exclaims at his Skill.

Ceil sighs, seeing the Demon Lord is unfamiliar with how children of Demon Lords work. {Answer: When Children of Demon Lords reach adulthood, around thirteen, they go through the process of Demonic Puberty.} The disembodied voice informed Rimuru more about what happened.

Rimuru looks at his Son, seeing the drastic change in him. "H-Harry, you…um…"

"You what, Dad?" Harry asked his Father, not sure what he means. "Why's your face in shock?" The changed Arch Mage asked, seeing the odd expression he was giving him.

"Um…H-Harry, let's head down to the dining room!" Rimuru laughs nervously, unsure how to approach this situation.

Harry glared at his Father, finding it annoying to get up this early in the morning. "Tch, fine. Just let me get ready." The dark green-haired Boy stood up from his futon and got ready for the day. Once Harry got dressed, he went down to get some breakfast.

Everyone stared at the young Arch Mage eating the breakfast that Alexis gave him. While eating, he was reading what was going on among Tempest.

Shinsha leans over to her Father, wanting to know what happened to her older Brother. "(Papa, what just happened to Onii-san?)" The Pink Slime asked her Father.

Rimuru leans over to his Daughter, answering her question. "(W-Well, Shinsha, this happens when Children of Demon Lords reach the age of Thirteen.)" He explains to the young Slime.

"So does that mean that will happen to me too?" Shinsha asked innocently to her Father.

"HAHAHAHA! Like I would let that happen!" Rimuru laughs, not wanting to think of a moody teenage Shinsha.

{Notice: You cannot stop age pro-}

'I didn't ask your opinion, Ceil!' Rimuru answered back on his Ultimate Skill statement.

Harry's eyes gaze over to his Family, finding it strange that both his Sister and Father are whispering among themselves. "What are you two talking about?"

The two Slimes looked at Harry, his head resting on his cheek and giving him a blank stare. "You two are whispering to each other loudly that I can hear it from here," Harry responded in a nontypical Harry way.

"Um, Harry…(ahem)" Rimuru cleared his throat, finding this to be the right time to tell him. "Do you…have you felt something has changed about you?" The Demon Lord asked his Son.

Veldora cleared his throat, "L-Like a sudden change in personality, perhaps?" The Storm Dragon asked.

Harry gave his Father and Uncle a questionable expression, unsure what he was getting at. "What do you mean, Dad, Gramps?" He asked. "I feel the same as before."

Veldora froze like he was turned to stone by what his Nephew said. "G-Gramps!?"

"That's not what I mea-"

"Good morning, everyone-Ah, I see the young master has reached his Demonic Puberty stage." Diablo entered the room, seeing the commotion before him. "To think that the young master is reaching adulthood soon will be a sight for sore eyes."

The Arch Mage looks at the Primordial Demon of Black, catching what he said, "Demonic Puberty?" Harry asked, unfamiliar with that term.

Diablo looks at both Rimuru and Veldora, seeing they haven't explained things to Harry. "Ah, so you haven't told Harry-sama, Rimuru-sama?" The Demon Butler asked his master.

Harry looks at his Father, eyes darting at him. "Told me what? Dad, are you hiding something?" He asked, raising his eyebrow at the Slime.

'Since when did Harry have that piercing glare?' Rimuru cleared his throat, seeing there was no getting out of this predicament. "Um, Son, you know that ever since you became heir of Tempest you know there were some changes to your being, right?"

"Well, yeah? I can do wandless Magic, have most of your Skills, and a Skill that's talking in my head." The young Heir explains to his Father, already knowing this stuff.

"So you do have an Ultimate Skill, I figured as much," Rimuru commented, assuming that since he inherited much of his and Shizu's Skills. "Anyways, Harry, Demonic Puberty is when a Child of a Demon Lord goes through a transformation." He explains slowly to his Son.

"It's like regular Puberty for Humans but more Demon oriented." Rimuru finishes his explanation to Harry.

Harry seems to be fine with the explanation his Father gave. His yellow eyes darted over to his Sister, curious about her. "So does that mean Shinsha will go through it when she's thirteen?" The Arch Mage asked his Father.

Both Rimuru and Veldora look at Shinsha, innocently blinking at the two. "Yeah, but don't think about it too much, Hars." Rimuru chuckles nervously at a teenage Shinsha.

"All right, then so this is natural right?" Harry asked rather maturely, "It's nothing to get concerned over,"

"Hold on, young master," Diablo interjects, being the one with the knowledge of these sorts of things. "Though you did change your appearance a bit, your Magicule or abilities have changed too." The Primordial Demon of Black explains.

Rimuru looks at Diablo, having a feeling about what he has in mind. "Diablo, are you planning to-"

"Of course my Lord," The Primordial Demon looks over to his young master, smiling at him. "Young master let's see if your Abilities have evolved as well in a little duel with me," Diablo suggested, being the one in charge of Harry's education.

"Eh?" Harry looks up at his Family's Buttler, hearing what he was suggesting-no, more like demanding.

Arena

Shinsha looks down at the Arena Battlefield, seeing her Brother wearing a simple white shirt and jeans, and black gloves. His hair shines like emeralds under the Sun, something that he didn't have before his change. "Papa, what is Diablo-san fighting Onii-san? Does it gotta do with Onii-san's change?" The Pink Slime asked her Father.

Rimuru looks over to his Daughter, he smiles at her and answers her question. "That's right, Shinsha. Since Harry has changed, we don't know how much stronger since then." The Demon Lord explains. "This is the best opportunity to measure his Abilities in person,"

"Can agree with you more, Rimuru-sama." Both Slimes look over to Hakurou sitting beside them with his blade prostrated before him. "The young master may have changed, but that doesn't mean his skills with the sword might be lacking," Hakurou stated,

"Sensei, don't belittle the young master like that," Benimaru commented, looking at his master below him.

The old Fair Oni closes his eyes, denying what the Flare Lord said. "I wasn't belittling Harry-sama, Benimaru-sama." Hakurou opens his eyes, seeing the Magic Lord exiting the other end of the Arena. "I was simply stating that the young master's skills with the Sword might change."

"Well whatever it is, I do hope the little boy and Noir will put on a show worth my while." Guy Crimson smiles, crossing his legs as he watches the Battle.

Rimuru stares at the Primordial Demon of Red, randomly appearing out of nowhere. "Guy, tell me…why exactly came all the way here to Tempest?" The Demon Lord asked his fellow Demon Lord.

Guy Crismon smiles at the Slime, "I have taken a personal interest in your Son of yours, Rimuru." The Demon looks over to Harry, waiting for the thing that caught his attention. "Thus it's my responsibility to see upcoming Demon Lords mature, and make sure they don't overstep the boundaries."

"Don't worry, Guy. Harry knows that his power can't give him everything." Rimuru smiles at the leader of the Octagram. "He's that kind of person,"

On the Arena's field, Harry twirls his Katana, curious about what he should do. "So, Diablo, what exactly do I need to do?" Harry asked his Tutor,

"Just try and strike me like when we're in our training sessions, young master." Diablo smiles, holding the Sword in his hand.

Harry sighs, going into his stance to strike. "Fine, if you say so, Diablo." The young Heir got serious, waiting for the perfect opportunity to strike.

A few minutes went by, causing some tension in the crowd. Soon in a split second Harry dashed forward, slamming his Katana into his Butler's Sword.

Diablo smirks, seeing the young master has taken the incitive to strike first. In response, he swung his body to escape the position that Harry has placed him in, "Interesting, your Accelerate Thought has increased, my young master." He stated.

"Well, I did take every account in my first strike. Like this one!" Harry launched himself at the black-haired Demon, slashing him.

Diablo blocked that strike as he proceeded to land a hit on the young Arch Mage.

Harry saw the move coming, prompting him to block with his blade. "NGH!" He slides back as Diablo put more pressure on his attack.

Back in the audience, everyone observes Harry and Diablo's duel. Shinsha blinks, quickly noticing that her Brother was quicker on his feet than before. "Onii-san is very fast. Was he fast before?" The Pink Slime asked,

"No, the Kid's senses have been heightened that he could quickly act in a split second," Guy commented, seeing the change in the young Demon Lord.

Hakurou nodded, agreeing with the Primordial Demon. "Indeed, the young master's strength has increased as well." The Fair Oni added, "With further training, I do believe he could be quicker and stronger."

Shion stood up from her seat, cheering on the young master. "GO HARRY-SAMA!" The Wicked Oni cheered on.

Back on the Arena battlefield, Harry was showing an impressive feat of Skills and endurance against Diablo. The young Arch Mage

Harry was pushed to a corner by Diablo, seeing that his Family's Buttler was going harder on him. "Not pulling any punches eh, Diablo?" He smirks at him,

"We can add cockiness to your change, young master." Diablo chuckles, taking note of his change of personality. He then leaps forward, thrusting his blade at the young Arch Mage.

The Arch Mage moved his head to the side, only receiving a scratch on his cheek. Harry then swiftly got out of Diablo's view before coming at him with Spells.

"Maximize!" Harry cried out as large flames burst from his palm, hurling toward the Magic Lord.

Diablo smiles, seeing the young master utilizing his new Skill. "Impressive," With a single slash of his Sword, the flames disburse, creating smoke spreading across the Arena's Battlefield.

Suddenly, the Primordial Demon of Black couldn't sense where the young master was. It's almost like he concealed his presence and hid his Magicules around him. "Where is-"

Diablo turned around, blocking the strike from Harry's Katana. He spun around and slashed at him, only for Harry to disappear again in the smoke.

The same thing happened from the side; this went on for a while until the smoke started to vanish.

"Well, this is very impressive, young master!" Diablo answers, liking how Harry was improving from the last time they spared,

Harry smirks, sliding back after striking Diablo many times. "I've been training under you for quite some time, Diablo." The Arch Mage commented, stepping back from his Butler. "By now I already know how you fight."

Diablo smiles, allowing the young master to come to him. Just as he was able to thrust his Katanna at him,

The Demon steps to the side, doing the exact same thing as Harry did to Draco last year. He placed his Sword under Harry's Katana before propelling upwards.

Harry's Katana slipped out of his hand, stumbling forward. "Tch," he quickly turns around only to have Diablo's Sword in his face.

"It seems despite your change, you still have a lot to learn, young master." The Primordial Demon smiles, looking at the young master.

The Arch Mage gave a displeased expression before chuckling at the end. "I guess you're right there, Diablo," Harry responded, having his Family's Butler offer his hand to help him up.

Everyone cheered for Harry having advanced in both his Skills and stamina before his evolution. They were all proud of him for living up as the heir of Tempest despite losing at the hands of Diablo.

Guy smiles, seeing all he needed to evaluate the young Arch Mage. "Your Son is an interesting one, Rimuru. I have never seen anyone quickly adapt to their new powers like Harry before." The Leader of the Octagram commented,

"Harry's a determined Kid, Guy," Rimuru commented,

"Keep an eye on him, I am really invested in Harry's Future." The Primordial Demon of Red smiles, placing both his hands on his side. "I'll be staying here for a bit for the Kid's Birthday. I take it there's room at the Hotel here?"

Rimuru waves his hand, standing from his seat. "Hai, hai, do whatever you wish, Guy." The Slime watched as the Leader of the Octagram left for the Hotel.

Shinsha smiles, leaning on the ledge after watching her Brother fighting their Butler. "Onii-san is getting stronger, right Papa?" The Pink Slime looks at her Father, "Papa?"

The Pink Slime watches as her Father and a few of his Subordinates were heading down to the arena. "Where are you going, Papa?" Shinsha asked.

Rimuru turns to his Daughter, "To congratulate your Brother, and also buy the others some time to get ready for tomorrow." He said,

"Ah, right!" Shinsha exclaimed, remembering what tomorrow is. "Tomorrow is Onii-san's Birthday!"

"That's right, now let's get Harry," Rimuru said, motioning his Daughter to follow him.

AN: How do you like it? Please leave a comment or review.