After MariaBell's death and Chaos Dragon's reform, Rimuru's life is peaceful again. But this is not over yet, because Mariabell's status is a princess of a Kingdom called Siltrosso, It will likely cause a massive alarm if this incident spreads to another kingdom.

Thanks to Souei, who gained intelligence regarding Western nations. there were no bigger threats than the Rosso family.

Rosso's family has a friendly relationship with a mercenary band called Apostles of Verte. Also, there were several organizations still holding on to their fang and waiting for the moment to strike.

Since Tempest had a good term with the Freedom Association and Holy Chruch as their benefactor, no one wanted to dare oppose them.

...

Peace was best, having no problem was a good thing.

Rimuru decided to visit Kurobee's workshop.

Rimuru and Kurobee greet each other. after that, Kurobee wanted to repost him with something good.

Kurobee brought out a boardsword which was a unique-grade weapon. A unique feature of it was three small holes on the base of the blade.

Nothing usual about the sword except its grade. Until Kurobee puts a marble in the hole of the weapon.

<<Report: Weapon: Boardsword has changed into Magic Weapon: Broadsword.>> - Raquael

(Ah! I knew it) - Rimuru

This is one of Rimuru's ideas for creating a weapon. Since he asks for it, Kurobee steadily researches this idea. When he was able to make it, Rimuru was amazed by his talent.

In this world, there were several ways of crafting magic gear.

Like utilize <Synthesis> and <Separation> from Wisdom King Raquael to affix magical effects to equipment. Kurobee also can do it well but Kurobee's disciples were not capable of suck powerful skill.

Yet, there is another way to achieve the same effect by casting it with magic <Engraving Magic>.  Dold, one of four Dwarf, was a skillful user of type magic and could easily cast it on the weapon.

Engraved magic gear could be infused with magic, so it could execute a certain magic. However, there was a limit to the number of magic that could be enchanted. At least, only two types of different magic could be enchanted. Moreover, it was impossible to remove the engraving effect after being enchanted.

It wasn't an easy thing to achieve, and it usually took an exceptionally long time. However, the growth of the weapons would often develop unexpected power.

There were a number of research projects to see. One of them is Spirit Core or Magic Marble. According to Kurobee, both Gabil, and Vesta were already researching the power core of Spirit Magic Core.

By enchanted magic stone with 4 primal elements earth, wind, fire, and water spirits.

All they need to do is adjust the size and power output of the magic marbles. With the properties of the magic power imbued in them, they became 'Spirit Cores,' which could be classified into four elements—earth, water, fire, or wind.

Naturally, the energy of these cores would run out. Once the magic contained within was depleted, they would be no different than purely decorative marbles. However, they could be recycled for repeated use.

Kurobee mentioned about combination of different spirits. But there were plenty of hazardous combinations. Magic marbles genuinely required some experimentation.

For example, a water spirit combined with a fire spirit reduces power. Even so, one water spirit marble paired with two fire spirit marbles results in a dramatic spike in power. This is not power increasing by a factor of three are talking about here, but a spike ten times more powerful than the original.

That said, it will need a lot of results.

...

Kurobee told Rimuru about something which revealed about his new sword. He gave the sword to him. 

The blade was as black as the midnight sky.

Rimuru thinks about infusing this sword with his mana which reveals something amazing.

"What! The b-blade is turning golden—no, that's not the only color. It's a rainbow. The blade is giving off the glow of a rainbow!" - Kurobee

RImuru had been gazing at his sword back in my room one day when it suddenly started changing hues.

Obviously, I was caught off guard.

The blade was giving off a rainbow-like sheen.

Gold was never used during the forging process, yet it gave off a shine brighter than orichalcum. That was why I decided to investigate the matter.

<Answer. This is the "Ultimate Metal" hihiirokane.> - Raquael

 Apparently, it was some very impressive metal that was superior in quality to the orichalcum he refined. Thus, he came to Kurobee for confirmation.

"T-this...what in the world is this? I can't even analyze it..."

"I think it is called something like hihiirokane?"

"Hihiirokane? D-does something like that really exist? It's said to be a mythical-grade metal that possesses immutable properties. I honestly thought it was something of a fairy tale..."

Kurobee was no longer just excited. He was stunned speechless.

This hihiirokane seemed capable of resisting the wavelengths of every single physical property. Normally, it wouldn't even reflect light because it simply canceled out the wavelengths within the visible light spectrum, which probably explained why the blade was pitch black. It could mask its unique properties from others as well—even from my <Analyze and Assess>. How impressive.

Moreover, it was also far sturdier than most average weapons, or should I say, its immutable properties meant that "It could not be destroyed." Even when it was damaged, it could be repaired by saturating it with mana.

In addition—

This sword was not complete just yet.

<...> - Beelzebuth

<!!!> - Raquael

Raquael immediately notices Beelzebuth who is staring at the sword. When Raquael tries to stop, it is already too late.

...

RImuru still holding his new sword. Suddenly, he senses Demonic energy from his hand.  A black tornado emerged from his hand and craving into his sword. 

The workshop started to shake crazy. 

Kurobee and others were shocked and tried to stop but were unable to.

Rimuru uses both of his hands to stop it. It continues until it reaches the tip of the sword. A black tornado instantly calms down and reveals itself.

A black sword with a glowing purple Aura around it. It shows demonic energy like a wild beast. Rimuru senses this sword infused with something different but familiar. 

<Report: Beelzebuth entered Master's sword which resulted change in properties and attributes. Additionally, it also gives the sword's ability to Corrosion which can target both Material, Spiritual, and Astral bodies.  Result: Weapon: Dragon's Blade temporarily changed Demonic Weapon: Gluttonous Dragon's Blade.> - Raquael

(What! Beelzebuth entered my sword without my permission. How?!) - Rimuru

<Report: Beelzebuth dislikes Master a lot. Result: Beelzebuth rebels again what I and Master want. Advice: The only way to stop is to directly approach Beelzebuth about this.> - Raquael

(Can you tell Beelzebuth to stop?!) - Rimuru

<Negative. Beelzebuth greatly despises us, especially Master. But since the sword isn't complete yet, Beelzebub will return to a docile state again.> - Raquael

A moment Raquael explained, his sword slowly turning back into its original shape which meant Beelzebuth would already go back into a docile state.

Rimuru and the rest were surprised by it. 

"Rimuru-sama! What happen!? The moment you hold the blade, something worse comes out from it." - Kurobee

"Sorry about this, Kurobee. There was something inside me need to care about. I promise I won't let this happen again." - Rimuru

"As long as you were safe, that's enough for us. Although there was something strange when the moment you hold it." - Kurobee

Rimuru listens carefully about what happened to my sword.

The sword Beelzebuth possesses into it like a vessel body. When the sword changed, He commented it already surpassed Hinata's sword, Moonlight Saber.

In addition, the quality of it was equal to or above the Mythical grade which was insane. Milim's sword, Tenma, was certainly one of them. 

Still, this only happened thanks to Beelzebuth. He thinks this incident should be kept secret. 

Hopefully, I can find a way to approach Beelzebuth and resolve this peaceful way. 

...

Author note: Hello viewer! I hope you all enjoy my story. I recently had a bad time in my life, so it will affect to writing skills even though you guys don't care about it.

Here's some idea when I write about Beelzebuth:

- I think Beelzebuth possesses a weapon that will become a Spirits Weapon which refers to Zanpankuto in Bleach.

- Beelzebuth and Rimuru likely fighting each other to prove Rimuru worthy enough to possess both Beelzebuth and Raquael.

- The battle will be inside Stomach's world or Imaganry's World like an inner world.

That's all the idea to make. Thank you for reading this short story.