It happened suddenly.

Issei was lounging around in Sona's house as usual (who, by the way, had been given a PC by her parents and just arrived this afternoon). Issei wasted no time in setting up the PC. While he wasn't a nerd, his father was one, so he knew some things.

Anyway, since Sona's house hadn't had an internet plan, there was nothing Issei could do about all the strategy games he could offer to Sona. So he just set it up to run smoothly and left Sona to her brand new PC (who, by the way, had some of the highest spec Issei had ever seen. Devil's richness was scary).

So since he had nothing else to do, his homework already finished thanks to the naggings of both Miyu and his mother, Issei was relaxing on Sona's comfy sofa. Ah, this was bliss.

But of course, nothing good could ever happen to Issei because it was at this moment that he heard a small explosion and smelled smoke.

With all the energy he could muster, Issei tried to find the source and found Sona with a smoking CPU of her brand new PC.

"How the hell..."

"I-It is not my fault," Sona tried to mask her nervousness, but it was clear to Issei. "Human World's computer is too fragile. Back in the underworld, a small accident with my magic would not result in this."

Issei just sighed and asked the obvious question. "What even happened here?"

"I did not turn off the computer. Then I practiced my magic here since that lesson here," Sona pointed to a book laying on her bed, "I was supposed to complete it by this month according to my schedule. But in my blind pursuit of finessing my tactical front, I neglected my magic training schedule."

Translation: Sona was too engrossed in playing strategy video games that she had forgotten her study. What a surprisingly mundane answer coming from a Devil who was using her magic to do things. Issei couldn't get angry at that, because he once did that too. But there was still one thing he didn't understand.

"How does practicing your magic leads up to the PC being blown out?"

"Ah, that," Sona winced and then frowned. Clearly, she was displeased that she broke her new gift. "I did not expect my magical output to be greater than it was before I practiced. My conclusion is that my magical power is growing. But I do not understand how or why. I did not practice anything before today. How perplexing..."

"Why are you getting confused? Shouldn't you be glad?"

"I am glad, but I have to redo all my magical study schedule because of this. Despite I am being diligent, having to adjust my schedule like this is quite vexing," Sona muttered to herself.

So she scheduled her own training, which she did on her own, with herself as the judge and motivator. Truly, she was too good to have known the lazy-ass boy named Hyoudou Issei, Issei wept in his own thought.

"Speaking of magical training, would you mind training me, Sona-san?" Issei found himself asking Sona.

"I would not be so sure. Devil's magic is fundamentally different from Human's magic. I might know how to teach you, but I would not be able to follow your training step by step because my magic skips several steps to arrive at the result."

Sona approached her bookshelf and picked out a book from there. She then handed it to Issei. "Still, if you are curious, here, it is a book on Human magic that I picked out when I was curious about the differences. I do not know how advanced it is or if it will help beginners or not, but maybe you can start there?"

Issei gave her a big grin, "Thanks, Sona-san. I'll read it! Although, I was looking forward to teaching you many strategy games in PC too... but well, something to occupy my time is here now."

After that, Sona was banned from practicing magic inside the house, so she moved towards the front yard. Of course, she did not forget to put up a boundary spell to keep the normal people walking outside to peer inside and see her practicing magic. Meanwhile, Issei was back on the sofa reading the guide to human magic that Sona gave him.

"Let's see... first chapter, basic math. Second chapter, basic geometry... isn't this just advanced math book?!" Issei closed the book with a 'bam' and slammed it to the sofa.

[Magic is diverse, Partner. Unfortunately for you, human magic is based on advanced math. Unless you changed your race, you have to deal with calculations if you want to manipulate the world.]

Issei looked down on his glowing left arm. "Ddraig! I almost forgot you can talk to me!

[Ouch, that hurts. Although I can't exactly blame you. The last few weeks are too peaceful. I have no need to interfere with your life. You were enjoying yourself.]

Issei's mind flashed back to the peaceful daily lives he had with Miyu and Sona. "Yeah. It was enjoyable. I'm really glad I got to meet Miyu and Sona-san. And you too, of course, Ddraig. Without you, I'd be dead now."

[Damn right it is. You are one of the most reckless users I've gotten, the worst part is that you're still young! You haven't lived your life fully yet! Don't throw your life away, you got it, Partner?]

"Yes, yes. I won't do it again. Probably."

[Still, what makes you interested in magic so suddenly, Partner?] Ddraig asked Issei who had opened a random page on the guide to magic book.

"We're still in season one. I am anticipating the surge of powered-up enemies that we wouldn't be able to handle."

[That argument again, Partner? You know that what you watched is just a tv show right?]

"Ddraig, you're supposed to be my partner! You're the same as Sona and Miyu and Sapphire! Why is my partner on this is only Ruby?!" Issei shook his left arm in the air.

[You do know that shaking your hand won't do anything to me, right?]

"It's the principle of the matter! Anyway, since I don't know when and how I will get a mid-season power up, I decided to explore it on my own. But who would guess that human magic is too complicated? Like, why would a circle inside a triangle which is inside a circle would trigger something in the spell? It doesn't make sense!"

[Your magical girl-muddled brain doesn't make sense.]

"How could you, Ddraig?! I don't want to talk to you ever again! Hmph!"

[...Calm down, he's just a kid. Calm down, he's just a kid.]

Issei closed the book for the second time. But this time he didn't slam it. He just put it on the table and laid down on the sofa. "I give up."

[That's fast.]

"Well, it's not like I'm some math genius who can gobble up the content of the book in five minutes. I know that I won't get magic, so I think I should give up and search for alternatives for my power-up. I can't just rely on you and the Class Card forever."

[If that's what you think is best.] Issei had a feeling if he could see Ddraig now, he would shrug his scaly shoulder.

Issei saw Sona entered the living room, "Ise-san. Miyu-san said that dinner is ready. Let us go. I am quite hungry after all the magic I spent."

Sona then looked at the glowing arm of Issei.

"Uh, yeah, me and Ddraig were just conversing," Issei answered the unasked question. "Say hello, Ddraig."

[Good evening, Sitri heiress.]

Sona straightened her back at that call. "Good evening, Welsh Dragon-sama."

"Don't be too stiff, Sona-san. Now let's go. I'm starving," Issei stood up from the sofa and both him and Sona walked towards Issei's house. "So your magical power really increased or was it just a one-time thing in the bedroom?"

Sona nodded her head. "My power is increased, yes. Do you think this is the side effect of Installing the Class Card?"

"Could be," Issei put a hand on his chin. "You mostly used Caster, after all. Her magic was scary."

"Her magic is also not something that exists in this world. Or they do exist but I do not know. Caster comes from Miyu-san's world after all. But this raises a question. You mostly used Archer, I wonder if Archer's skill in archery bleeds into you, now?"

"I dunno. Never been interested in archery before."

They arrived at Issei's house and ate dinner in contemplation.

It was after dinner when Sapphire and Miyu came into his room.

"Ise, Sapphire detected a Class Card manifestation."

Issei grinned. "I was right! Take that, you doubters!"

"Now is not the time, Issei-sama. Let's go to Sona-sama's house. No doubt Onee-sama also detected it," Sapphire tried to steer the conversation back.

"I also have no doubt that Ruby is grinning and bugging Sona about this now. I can't wait to do the same."

"I'll think up an excuse for Mother. Sapphire, you should go from the window. Let's go, Ise," Miyu grabbed Issei's hand and ran downstairs.

Seeing him and Miyu in a hurry towards the exit, of course, his mother asked the obvious, but Miyu said that they had something to do in Sona's house and they didn't want to be late convinced his mother to let them go.

"Man, Miyu, your act is too good. Completely playing Mom like that."

"Technically not a lie," Miyu replied back as they exited the Hyoudou household. "We do have something important to do in Sona-san's house, after all."

When they arrived outside, Sona was already standing there waiting for them. Her face contorted in annoyance of the floating pink magical girl stick who circled over her. Issei was about to open his mouth when Sona covered her ears with her hand and closed her eyes.

"I am sorry, were you about to say something? I did not catch it."

Issei had the biggest grin he ever had. He then turned his attention to Ruby. "My buddy Ruby-chan!"

"My partner Ise-chan!"

They did a high five.

"You can gloat later, Ise. Finish the problem first," Miyu said and the three plus two got into focus.

"Right. What the hell, Ruby, Sapphire?! I thought there are only seven Class Cards?!"

"You are correct, Issei-sama. This is not something that we know," Sapphire started to explain. "However, our detection spell is not wrong. Somehow there is an eighth Class Card."

"Let us not waste any time and go there," Sona proposed. "Ruby, you detected no strange happenings before this, correct?"

"That's right, Little So-tan. Everything is peachy until suddenly my sensor detected a new Class Card," Ruby answered as everyone was walking towards where Ruby and Sapphire felt the Class Card was.

"So is your Grand Master wrong, then?"

"Either he withholds information or he does not know, and I don't know which of the two is worse when you consider the implication," Sona offered her theory.

"I think he does not know," Miyu speculated. "I still remember when Onii-chan sent me here. He has seven cards in his possession."

...

"What if it's someone from your dimension, Miyu?"

Miyu stopped moving.

"...Possible," Sona concluded. "I don't like it one bit, but it's possible."

Issei thought there was something akin to fright on Miyu's eyes, but when he blinked, it was gone, replaced by a determined look that was not unfamiliar to him.

(It was a look he always had when he decided to do the impossible.)

It was when he knew that Miyu would be okay. One glance at Sona and both decided to not say anything about it anymore.

The rest of the journey went in silence.

When arrived at the destination, they didn't waste any time transforming into their magical girl form. Unfortunately for Miyu, even after all these times transforming, Sapphire still could not make use of the skip function, therefore Issei still had to close his eyes when she was transforming, unlike Ruby who skipped Sona's transformation sequence.

"You done? Let's enter the Mirror World!" Issei asked around when he felt the light from the transformation faded. Issei then latched himself into Miyu as the two Kaleidosticks performed the dimensional shift.

What greeted them wasn't the mirror images of the scenery that they saw before.

"W-What the hell?!" Issei asked no one in particular.

Indeed. As far as his eyes can see, everything was covered in ice, including the big black shadowy thing frozen in a block of ice on the corner of his eyes.

"O-Onee-sama, what are you doing here?"

Onee-sama? Issei turned his head towards Sona only to see that she was glomped by Serafall who was happily laughing.

So the frozen landscape...

"It was all hers," Miyu hollowly spoke as she came into the same realization that he had.

"Oh, Ise-kun and Miyu-chan are also here! Yay! The full team is here!" Serafall dragged the unwilling Sona towards them. She then took them into her embrace.

While Issei didn't like the suffocating feeling, he loved the soft sensation of Serafall's breast on his cheeks. His path in life was truly the correct one.

"Serafall-san, that shadowy frozen figure..." Miyu trailed off, looking at the suspected blackened Heroic Spirit frozen in a block of ice.

"Yes yes, I don't know what will happen if I kill it without using Ruby-chan, so I just freeze it until you guys came."

"How did you enter the Mirror World without the Kaleidostick, though?" Issei pointed out something weird.

"It's all thanks to Ajuka-chan here!" Serafall pointed her fingers towards the figure standing calmly observing their interaction.

"A-Ajuka Beelzebub-sama?!" Sona instantly bowed her head in deference.

Beelzebub... Beelzebub... Issei felt like he had heard about that name from Sona when she explained about the Devils, but he couldn't remember when.

"One of the four leaders of Underworld alongside Serafall-san," Miyu answered his unasked question. Was his face too easy to read? Wait, leaders?

"Um, should I bow or something? Considering I'm not a Devil or anything."

When Issei finished asking the question aloud, Sona bowed her head even further, while Miyu just sighed and muttered this was just so Issei. Serafall was laughing at the situation.

He didn't understand. He was not wrong. Why were their reactions like that?

Said man was looking straight at him with a stoic face, then turned his attention to the others "No need. But as Serafall said, I made a Class Card detection device and detected a signal coming from this place. I did question her since she said that there should not be any... spirits anymore. Since both of us are curious, we entered this place."

"Are you saying you know how to enter the Mirror World?!" Ruby jumped from Sona's grip and floated around the man.

"I didn't. But I analyze the phenomenons around this place and came to the conclusion that I could. So I enter this place."

...

That was...

"So coooool!" Issei looked at the other adult in the Mirror World starry-eyed.

"Then after that, we were greeted by the guy there rudely!" Serafall interjected as she began her tale.

The light from the magic faded as Serafall and Ajuka took a step inside the Mirror World.

"So this is the Mirror World containing the Class Card manifestation, huh? Quite interesting use of dimension space spell."

"Stop it with the buzzwords, Ajuka-chan. What does your detection device say now?"

The Device was still beeping and displayed that they were currently in the correct position to see the Class Card manifestation. So where was it?

His instinct honed from the war ages ago told him to move, he obeyed it to see that the place he was before was covered by several bladed weapons.

"You! You're rude! At least greet us first as a proper villain!" Serafall threw several icicles back at the source of the weapons, that was, a shadowy figure standing not far from them. It was no doubt, the Class Card manifestation from what Serafall described before.

The icicles aimed at it were thrown off course by several bladed weapons coming from a golden ripple in the air. There were swords, spears, lances, halberds, axes, knives, and many more things ready to be thrown at will.

Not to be outdone, Serafall also created icicles in varying shapes to match the Class Card manifestation.

This...

In the Civil War, he had witnessed several scenes that mirrored what he saw currently. It was when Serafall took the frontline by storm. In those times, he always relegated into a support position instead of the front line. He felt that this would be like that, especially now when Serafall had made it a personal vendetta against the manifestation.

So Ajuka Beelzebub went to work. Since he played support, he guessed he could help Serafall controlling the icicles.

The Servant's weapon and Serafall's icicles both rained down. He steered those who left Serafall's control and twisted it towards the Servant in black.

However, it wasn't that easy. The Class Card manifestation had complete control of his surroundings. It was as if he had eyes behind his head.

"Not enough, huh?" Ajuka began to calculate how to turn the weapon it discarded back into him. Before he even lifted the weapons off the ground, the Servant realized what he was doing and exerted control of all of its weapons, dispossessing Ajuka of its weapons. The weapons formerly under his control dissipated into a black mist and gone.

He took a single glance at Serafall. She was still pouting at the Servant and this time she didn't throw icicles. She straight-up created blizzards.

Classic impatient Serafall.

The blizzards and subsequent hails frozen the parts of weapons outside the golden ripple.

The temperature now was very freezing. If Ajuka didn't adjust the area around himself to normal temperature, no doubt he would freeze. Serafall had done this several times in the past (and froze people too).

"Take that, you rude little villain!" Serafall made a pose. "Now for the finisher!"

Serafall was about to finish the Class Card manifestation. But Ajuka didn't know what would happen if Serafall defeated the Class Card without using the magical girl stick she used before.

Rather than looking forward to the unknown phenomenon that will happen as a scientist should, Ajuka played it safe. This matter, after all, concerned other worlds. And the being closest to the other worlds? Great Red. He did not want to incur Great Red's wrath.

Thus, Ajuka stopped Serafall from finishing the Servant.

"Serafall wait. We don't know what will happen if you kill a Class Card manifestation without using the magical girl stick."

That stopped Serafall on her track.

"You're right! And besides, it would help no one if we kill it now. Let's give the experience to the future holder, shall we?" Serafall winked.

Future holder... Serafall's little sister and her band of friends, huh?

"That' s fine to me."

In an instant, Serafall froze the entire Mirror World.

"Wait a minute!" Issei suddenly shouted, cutting Serafall's words. "If you froze everything why is Beelzebub-sama over there fine?!"

"Eeh, Ajuka-chan can do anything if he wants to," Serafall shrugged. "Shielding himself from my area spell is easy peasy."

Said man was just stoically looking around.

"So are you guys ready to face the anomalous Class Card?" Serafall grinned asking the question.

"Of course! Isn't that right, Miyu, Sona-san?" Issei excitedly answered and sought confirmation from his peers.

Miyu nodded while Sona replied with a firm yes.

"Don't forget that you also have me and Sapphire-chan!" Ruby declared as the three of them prepared each card they wanted to use.

Issei was, once more, Archer. Sona still used Caster, while Miyu went back to Rider. Issei noted that everyone chose versatility over overspecialization.

Issei felt that he was being stared by Ajuka more than the others.

Miyu put the card on Sapphire, and Sona did the same on Ruby. It was time for him to summon the Boosted Gear. He raised his left hand as it glowed with emerald light.

There was a small gasp of breath coming from Ajuka that Issei missed.

When his lower left arm transformed into its draconic counterpart, Issei put his Class Card on the emerald jewel.

Then the three of them invoked at the same time.

"""Install!"""

Bright light covered the three of them as the power inside the Class Card spread around their entire beings, changing their very nature.

"Interesting," Ajuka muttered on their side as he observed the Installation process.

Now after the Install was finished, they each clad in their respective Heroic Spirit uniform looked towards Serafall.

"We're ready."

"Okay, I'll release the ice in three, two, one, now!"

The ice around them melted off and their confrontation begin!