C.S.O.

 Ruko, Flamia, and Chiaki are heading to another world, the Celestial World, also known as CSO, with their in-game characters or within that world.
Their current goal is to find Kuro and Mea, who are currently together.
With the skill or feature to locate friends in the game, they know that both of them are in the third world called Alfheim, specifically in the floating city named Junshu.

“We can reach that city with teleportation items, but I only have two of them.
What about you?” Flamia asked.

They arrived in Gianta City when they first logged in, and it took them an hour to reach Junshu City by flying.
Although they would encounter monsters along the way, it wouldn't be a problem with the levels they currently possess.

The problem might arise from Liber or curious players.
However, considering who they truly are, no one would dare to cause any trouble.

“I don't have any.”

“..me neither.
Should we buy one in the nearest city?”

“That's a good suggestion, Ruko-chan, but I don't think we need it.”

“What do you mean, Chiaki?”

“Kuro-chan and that promiscuous woman are still in Junshu City for a long time.
I think they're waiting for us.
That means we don't need to rush there.”

“…”

“…”

“What we should focus on now is how to persuade Kuro-chan.
Considering his nature, I don't think it will be an easy task.”

Chiaki (Chika) glanced at Ruko (Anna) with a cold gaze.

“Do you still have any secrets you haven't told us, Ruko-chan? Why didn't we discuss it before meeting Kuro-chan?”

“..aha ha…
Chiaki-chan, for some reason, you are scarier than usual.
I knew you would still be angry.”

Of course, Chiaki is still angry.
She has been deceived and played with all this time.
If she wasn't a patient person, she might have taken her own life.

“I'm also curious,” added Flamia.

Ruko fell silent for a moment and let out a small sigh.
Then she started to speak.
If it's called a secret, it can actually be said not a secret.
..we God Slayers are dangerous entities, and of course, the government knows our identities and…”

“Did they keep it a secret?” Chiaki interrupted.

God Slayers and Fallen Gods are more dangerous existences than nuclear weapons.
If the world knew there was a weapon more dangerous than the most powerful human weapon, no one could imagine what would happen to the world.

The world governments knowing about their existence is considered normal.

And of course, that means-

“..Wait, did you mention that your government already knows the truth about CSO?”

Ruko nodded in confirmation.

“The government formed a special team to handle CSO issues.
It can be said that CSO is a phenomenon that is unique and happening for the first time in the world.”

Fallen Gods appear when humans lose their faith or forget the existence of certain gods.
But CSO, which is based on Norse mythology, emerged in its complete form and as a game that anyone can enjoy.

If used as joke material, it might end up becoming a completely unfunny joke. 

“Although the goal of the god Odin in changing the rules of the world was only to seal and destroy the Demon God, from the government's perspective, it is a dangerous action as it involves humans from this world,” Ruko continued. 

“But so far there haven't been any problems, and security has been guaranteed for the past two years.
Even though we use most of your souls, we have never endangered you.” 

“Flamia, how can you say that?”

 “…eh? Wasn't I ju-” 

“On what basis does Chiaki-chan say that using our souls is something safe?!” Flamia fell silent.
She tried to reconsider what she had said, and in the end, she couldn't find the right answer at all. 

“Ehe he..
as far as I remember, we was indeed not given an explanation about the magic system in the CSO world.
In my opinion, only the god Odin knows all the systems in CSO, but I don't know where he is.
I don't think my siblings know either.” 

Other gods besides Odin have been confirmed to exist.
One of them is the god Hal, who guards the realm of death and is now in Nilfheim.
Although it is not yet known, there is still a possibility that Odin is not in the CSO. 

“What you're saying makes sense, but I think we should think about this more seriously.
Unfortunately, we don't have time to think about it.” 

Ruko and Flamia nodded in agreement.
Their gaze was only directed toward a floating island not far in front of them.
They had arrived. 

“We should discuss this later after everything returns to normal.” They then accelerated their flight, even though it would drain more of their MP.
Upon arrival, they easily found Kuro and Mea, but they sensed an unpleasant aura between the two. 

“Onii-chan.
M-Mea-san?” 

“Hm? Oh..
so she's Kuro's new wife?” 

“…”

There were no friendly gazes from Chiaki. 

Mea smiled slightly upon seeing who had come.
Although their appearances were different from their original ones,

Mea smiled slightly upon seeing who came.
Despite their different appearances from their original forms, Mea didn't need to think much to know who the three of them were.

“Nice to meet you, my name is Mea Chihaya.
You can call me Mea or Chihaya.
I don't want to force you.”

Mea showed her friendly attitude, but it made the three of them unsure how to react.

Mea was a stranger to them, and they also didn't know what had happened between her and Kuro.

Mea smiled faintly and looked at Kuro.

“Kuro-kun, I understand why you enjoy playing CSO.
You have a good wife.
Ah…
I forgot, I'm your wife now too.
Eh he he…”

“…”

“….”

“…”

“I'm happy because I also like you.
If there was a world that could make everyone happy, I would choose that world.
…But Kuro-kun, as I said earlier, the person I like is not you.”

Mea's ring suddenly glowed.
At the same time, her body began to disappear.

The three of them realized that Mea was returning to Earth.

“I guess this isn't the right time for us to talk.
Goodbye for now.
I hope we can be close.”

Mea vanished, leaving only Kuro, who hadn't looked at the three of them since earlier.

The atmosphere around Kuro became strange and tense as Mea left.
Ruko, who possessed different powers, could sense that something had happened to Kuro.

(…What really happened while they were here?)

The sun rose higher and emitted its strongest light.
But slowly, dark clouds came and covered it.
Alfheim, which was always bright, now became unpleasant.

“..Onii-chan…”

Kuro didn't answer and remained silent.
He gazed at the sky, and suddenly, black wings spread from his back.

Kuro flew around and looked at the three of them with his red eyes, which were the manifestation of demon eyes.
But unlike his gaze until now, Kuro's eyes now only had a single box.

This difference didn't hold much meaning for Flamia and Chiaki, but for Ruko, it was-

“Onii-chan…?”

“….”

“……Could it be that you….”

Kuro didn't answer, but instead, he smiled faintly.
It was at that moment that his sharp white fangs became visible in his mouth.

For Ruko, it was evidence of an unwanted event.

(Damn, I didn't expect it to happen this quickly.)

As they pondered all the worst possibilities, a sword suddenly appeared in Kuro's hand.

It was the usual katana that Kuro used, but it emitted a strong electric current.

“Takemikazuchi the Origin Thunder.
I didn't expect Kuro to obtain that rare item.”

Flamia was impressed, but at the same time, she summoned the god slayer Misteltein in her hand.

“I have a really bad feeling about this…”

Not only Flamia but also Chiaki and Ruko felt the same.
They all assumed defensive positions.

It didn't take long for them to prove their instincts right as a thunderous cloud suddenly enveloped Junshu City.

And at that moment-

“[Thunder Rush Rain]”

Finally, a thunderstorm rained down on Junshu City with tremendous force.
And of course, the three of them were caught in it.

******

After the thunderstorm subsided, all that remained was a completely destroyed city.
Fortunately, Junshu City was uninhabited, so there were no casualties.
However, the total devastation that occurred would leave many people curious about what had happened.

Please note that translation can sometimes be subjective, and the context of the original text may impact the accuracy and interpretation of the translated version.

In one corner of the triangle, a crimson-colored shield was visible.
It was one of Flamia's skills called [Flame Aegis].
It could be said that it was her strongest defensive skill, but the defense had many holes in various places, as if it could be destroyed at any moment.

“Ugh…
I didn't expect Kuro's attack to be this strong.”

Thanks to their status as husband and wife, Kuro's attacks wouldn't affect their HP bars, but they would only impact their equipment.
The armor they were currently wearing suffered severe damage, and using their [Auto Use] skill, they replaced it with new equipment.

“To be honest, I still don't understand why Kuro attacked us.
What is he thinking…? Buuu…”

Chiaki and Ruko understood what Flamia was feeling, but precisely because of that, they had to find out.
Kuro had disappeared from their current location.
Ruko tried to use her tracking skill and her special privileges as Kuro's wife in CSO, but she found nothing.

“I think Onii-chan is no longer in Alfheim.
And I think he has blocked all contact with us.”

The tracking feature could only be used within the same world they were in.
And the special privileges also included privacy, so partners or companions were not always together.

This was one of the weaknesses of the husband and wife system in CSO.
However, some considered it normal.

“What should we do now? I actually don't want to say this, but is that the Kuro I've known all this time?”

The kind-hearted, carefree, and sometimes foolish Kuro was the person she loved.
In her eyes, Kuro was someone who cared for their family and was precious to her.
The Kuro she loved would not attack her with such force as before.

“Of course not.
Kuro-chan wouldn't show that kind of smile and face.” Chiaki paused for a moment, as if recalling something.
“No.
Although I don't remember it clearly, Kuro-chan used to always smile like that…”

“What do you mean?”

“I still don't know, but…”

“We don't have time to discuss this,” Ruko interrupted.
“One thing you both need to know is that we are already too late.
The worst event we wanted to prevent has already happened.”

Flamia and Chiaki were shocked.
They understood what Ruko was saying, but for some reason, they still couldn't believe it.
They even started, but the event they wanted to prevent had already occurred right before their eyes.

“…Ruko-chan, you don't want to say that…”

“Unfortunately, your guess is correct, Flamia-chan.
Onii-chan has become a demon.
And the worst part is, we may not be able to restore Onii-chan to his former self.”

******

Several days had passed since that incident.
During that time, the three of them still hadn't met Kuro or knew his whereabouts.

During that time, Chiaki and Ruko continued to search for clues about Kuro in the real world, while Flamia searched for Kuro in CSO.
With the Ring of Rinne that allowed Kuro to easily travel between the two worlds, they were truly struggling to find clues about Kuro.

As a result, Chiaki and Ruko found it difficult to concentrate, even though exams were approaching.
And various other problems emerged one after another.

On Tuesday, March 2, 2040, the three of them gathered at their home in Midgard to discuss what they should do.
The place they discussed was, of course, the large bathing area in one of Flamia's palaces.

Being naked and open with each other improved their relationship.
That was the reason why they did this.
For the sake of their husband, they set aside all differences and united.

It could be said that this was the second time they faced a major problem because of Kuro, but it was also thanks to that that their relationship as a trio had improved.

At the same time, they also gained many friends like Angela and Horizon.

“From your expressions, I can guess what happened.”

Without saying a word, the three of them let out a heavy sigh simultaneously.

Silence ensued for a moment because no one knew how to start.

But suddenly, Chiaki's face showed an expression as if she remembered something.
Something important.

“Ruko-chan, can I ask something important?”

“Hm?”

“Is it dangerous when merging with a demon?”

“….Chiaki-chan, if it's not dangerous, then there's no reason to prevent it from happening.”

Flamia listened as well.

“When a demon merges, not only their souls merge, but their bodies also merge with the power of the demon.
A human body using demon power will eventually be unable to withstand power beyond human capabilities and, in the end, that power will damage the user's body.”

Ruko's face turned pale.

“This has happened many times before, and in the end, our family members died young.
And that's why I don't want this to happen to Onii-chan.
I don't want him to die and leave us.”

“….”

“….”

Ruko's words were not pleasant to hear.
But now they understood why Ruko seemed rushed and was the one most eager for Kuro to return, even if it meant losing his memories.

It was better to live and return without memories than to lose everything forever.

It wasn't the wrong decision, but was it the right course of action?

“That's all I wanted to say, Chiaki-chan.
Flamia-chan…”

Silence returned, but unfortunately, it didn't solve their problems at all.

Flamia let out a small sigh and submerged herself into the bath.
It was one of her ways to think more calmly.

(Kuro has a demon soul within him.
He has now merged with that demon, or you could say the demon soul has taken over his body.)

Flamia wasn't the type of person who thought too much, but when she could calm herself, her thinking ability could rival that of the most genius person in the world.

(A vulnerable human body won't be able to withstand the power of the demon residing within it.)

Flamia recalled everything that had happened and everything she had experienced, including when she was attacked by her own husband.

There was no doubt that the smile and eyes were not what Kuro had shown all this time.

…but for some reason, why did Flamia feel something odd about all of this?

She racked her brain and thought hard.
In the deepest part of her heart, she still believed in her husband.
No, it was precisely because of that belief and trust that they had built their husband and wife relationship.

(….)

No matter how much she thought, all she found were dead ends.
But she believed in Kuro.
Whatever Kuro did, it must have a reason, and there must be a path to a happy ending.
Even though he was now merged with a demon.

But what? The path shown by Kuro was difficult and treacherous.

A human body with a demon soul.
God Slayer.
Formidable power (Kamikiri-ryu) of Kuro.
Another personality.
Fallen God.
CSO.
Ring of Rinne.
Skills.
Fusion.

“!”

After thinking hard, Flamia realized something important.
A way.

“…Fuahh…!”

Flamia resurfaced and approached Chiaki and Ruko, who were engrossed in their conversation.

“What's the matter? Did you already know where Kuro-chan is?”

“If you don't help us find Onii-chan quickly.
We plan to do it again after this.”

Flamia chuckled softly.

“Hey…
I want to ask you something.”

Both of them stared at each other and then turned their gaze towards Flamia with cold eyes.

“Aha ha…” Flamia was used to that.
She continued, “Tell me, what do you think of Mea?”

“A promiscuous woman.”

“A vixen.”

Cold and merciless direct answers.
Was Mea that terrible in their eyes?

“…..I can understand why you think that way.”

In the deepest part of her heart, Flamia felt the same way.
Their current situation was the best.
Sharing Kuro with both of them was already difficult for her.
And now she had to share him with another girl.

Those two might need more time to accept Mea, and worst of all, they were confronted with a situation like this.
It was no wonder their moods were bad.
Very bad.

“…but come on.
I don't think Mea is that bad.
Besides, we don't know her yet.
Chiaki-chan, even though you're in the same school, you don't know her either, right?”

Chiaki turned her face away but didn't deny it.

“But why are you asking? Don't you think that promiscuous woman might be hiding Onii-chan?”

If Kuro were in the real world right now, Ruko would easily find him because Kuro emitted tremendous energy.
Or you could say it was the effect of his power as a God Slayer and a half-demon.

Flamia denied it by shaking her head.

“I'm sure Kuro is in CSO, but because this world is vast, we're having difficulty finding him.
But I know, even though Ruko-chan says we have only a little time, I believe Kuro knows his own condition better than anyone.”

“….”

“….”

Flamia's words made both of them realize something important.

Kuro was someone who had merged with a demon.
How could he not know that he would die if left in that condition?

“Do you think Kuro will die easily? He has died before, and he came back for the sake of both of you.
What's the difference between then and now?”

“….”

“….”

“Not dying means losing his memories as a human.
But don't you think that might be the same as death for Kuro?”

They fell silent, but their eyes showed that they understood what Flamia wanted to say.

They had to trust Kuro that he wouldn't die easily, even though he now seemed like a ticking bomb ready to explode at any moment.

“That's why I think the first thing we should do is meet Mea-san.
Honestly, I feel like all of this is related to her.”

They both remembered that everything started when they met Mea.
Upon reconsideration, it would make sense if Mea was involved in all of this.
And of course, to resolve everything, they might need Mea's power.

“…I don't like this.”

“…”

Of course, they wouldn't immediately agree or easily accept Mea.
But if they involved Mea, it would mean accepting her into Kuro's harem.

“You both understand that my words are not wrong, right? So I think it's decided that we will meet Mea-san.”

“..Tch..”

“I hate it when you say that.”

Although they were not pleased, if it had something to do with Kuro, both of them would never refuse.
Especially when it concerned Kuro's life.

At the same time, Yamato and Kuroyuki were in a remote area in one of the mountains.
They were on a mission to kill the Fallen God that had destroyed a village.

The Fallen God they were facing this time was not too powerful, but the village in the mountains was completely devastated and uninhabitable.

Yamato took out a cigarette and lit it.
He inhaled and exhaled white smoke.

Not far from him, Kuroyuki gazed at the sky with a sad expression.
The cold wind and weather seemed to reflect her current state of mind.

“….Are you still worried about them?”

Yamato approached and embraced his beloved wife.

“Of course, I'm worried.
We have burdened them too much.”

Yamato took a drag of his cigarette.

“..And besides, I still feel guilty for lying to them about Kuro.
As parents, I feel like I have done something cruel.”

“You don't need to worry.
Kuro is our son.”

“…”

“He may become the greatest disaster for humanity if he makes a wrong move.
But at that time, it is our duty as parents to stop him.”

“..yes, you're right.
I suppose there's no harm in trusting them.”

Suddenly, the ground split open, creating a deep chasm.
Dozens of houses sank into the ground, and no one could escape the darkness emerging from within.

Both of them were unharmed and flew in the sky, witnessing everything crumble.

“Tch..
I thought I killed it, but is this the power of Tinia, known as the ruler of the earth? Don't joke with me!”

The figure of the final monster finally appeared, resembling a giant stone and emanating a powerful aura of darkness.

“Unfortunately, there seems to be something strange about this Fallen God..”

“…I agree with you.
Fallen Gods don't emit this kind of dark aura.”

Yamato sharpened his gaze, deep in thought.

Fallen Gods would attack with the goal of reminding humans of their existence, but most of them only caused destruction.

Although the task of the God Slayer was to fight against Fallen Gods, in reality, they were more focused on minimizing the damage caused by the rampage of the Fallen Gods.

But the true reason was that no one wanted these two disastrous beings to fight and destroy everything.

Fallen Gods indeed caused havoc, but that didn't mean they were entities that had to be eradicated.
However, the Fallen God standing before Yamato and Kuroyuki could no longer be called a Fallen God.

…it was more appropriate to call it a demon.

“Damn!! We have to use our full power to defeat it.
This time, we'll annihilate it, Honey!”

“…your bad side is showing again, Sweetheart.”

One of their eyes changed color, and at the same time, a sword appeared in each of their hands.
Their swords were magical weapons that actively responded when they activated their powers.

This was the power of the God Slayers, who had mastered their abilities perfectly.

“This will be an enjoyable battle…”

“…let's feast.”

As if they had transformed into different people, another battle had begun.

Meanwhile, Kuro observed the fight between Yamato and Kuroyuki and the rampaging Fallen God with a creepy smile.

He even enjoyed the snacks he brought along.

“Phew…
they are truly amazing…”

Someone approached and sat next to Kuro, taking some snacks and eating together with him.

Both of them watched from a hill that was far enough from the battle location.
Despite the intense battle, they didn't have to worry about being affected by the attacks.

“They are your parents, why do you let them and instead watch them? You are indeed a demon.”

“Thank you.
I am indeed a demon.”

Kuro smiled and showed his two fangs.

“But don't worry.
The demons residing in their bodies are Gremory and Phoenix.
They won't lose to a Fallen God of that level.
Maybe this is actually a good exercise for them.”

“I…
I don't know if it's some kind of new sport, but I don't want to watch this any longer.
Can you take me home?”

Kuro sighed.

“Didn't you yourself want to see the battle between the Fallen God and the God Slayers? Come on, stay with me a little longer, Mea.”

“Listen, I'm not officially your wife yet.
Don't boss me around too much.
Now, I want to go home.
If it takes too long, Chiyo will worry about me.”

“Fine…
in that case.
Let's go home.”

In an instant, light enveloped them, and they disappeared as if swallowed by the earth.

Why haven't Flamia, Ruko, and Chiaki found Kuro yet? The answer is simple.

Kuro can now use all his demonic powers and all the powers he obtained from CSO.
Who could find or stop a person with such immense power?

…perhaps no one.