A Hero must not falter.

Yuuna was a Hero. She understood the weight of her duty perfectly well and believed that even if things seemed hopeless, she was certain it will be fine in the end. Her body could still move, her spirit was still unbroken, and her feelings had yet to change.

That was why, exactly because she knew all too well about herself that she faced the combined monstrosity born from her failure without a change of expression.

Maybe she simply didn't notice. Maybe she could have done something before the situation escalated to this point. Maybe looking at the mirror might have allowed her to change her opinion, but it wasn't the time or even place to do that.

"Girls!" Fuu called out. "Retreat! We don't know what the thing is—"

Yuuna's eyes widened as they reflected a chain of torches lighting up around the ring behind the Vertex.

Before she knew it her body had moved and she leaped back as a rain of fire poured down.

Karin followed right after her but her speed was greater than Yuuna. She should have outpaced her by now but those flame bullets chased after her and closed in at a moment's notice.

"They're even faster than before!?" Karin gasped and turned around to cut through three bullets with wild abandon.

However, everyone's strength had already dwindled. Even Yuuna was feeling fatigued after the prolonged battle, and Karin was the first victim to be engulfed by the flame arrows.

"Karin-chan!" Yuuna cried out.

She heard cries and screams. She looked to her other friends and she saw them struggling to escape spheres of water and blasts of compressed winds.

Itsuki was the second one to be hit by the wind bullet. Her body crashed against a vine and bounced off it as swarms of water spheres made their ways toward her.

An unrestrained roar came from Fuu as she jumped and shielded her little sister from the barrage of attacks. Both of the Inubouzaki siblings were consumed by the detonation of the water spheres.

"Itsuki-chan! Fuu-senpai!"

Yuuna had to help them. She had to fight and protect them, but…

When she realized, she was the only one left. Her limbs were tired. Some parts of her mind wished she could sleep.

As the towering figure of the Vertex stood before her, something moved from behind it and Yuuna crossed her arms to shield her face and chest.

Gyuuki flashed into existence at the same time as a bladed appendage pierced through the sound barrier. The Fairy barrier protected Yuuna just in time, but the shockwave passed through and she was easily blown away by it.

Yuuna's head and right arm hit the vines first. Something cracked within her, and her back smashed into a vine that stopped her for good.

"Kah…" The girl coughed out a red liquid.

All she could see with her hazy consciousness was a blurry mess. Where was she? What had happened? Her head throbbed in pain and she could only recognize vague figures in the distance.

There, floating and moving away as if having no interest in checking whether or not its enemies had died for good. The Vertex moved as if… It was as if …

"…No…" Yuuna murmured, and she clenched her still feeling hand. "Can't… go… Don't go there…"

You can't go there, the girl thought as images of a girl and a boy flashed in her mind. I won't allow you, I can't allow you to hurt them.

Her right arm was numb, while Yuuna couldn't feel her fingers moving at all.

Still the girl rose to her knees and stood up.

Her eyes couldn't see very well. Her eyelids felt so heavy that it would probably be better for her to close them and sink into a deep slumber.

Still the girl walked forward, even though she couldn't maintain her balance.

Words of defeat were being whispered in the back of her mind. It might be better to let it go. It would be easier for her, right? There was nothing wrong with knowing her limits, right?

The girl came to a halt, her long ponytail fluttered in the wind.

The Vertex stopped moving and turned around. A cold shiver ran down her back as if the monster was 'looking' at her. Before the monstrous abomination and before she could muster the strength to move any further…

A curtain of fire scattered and rained down upon Yuuna.

Monsters.

Tougou had never thought she would be conducting a Youkai Extermination while doing her duty. It certainly was a new experience and there was a different feeling in fighting against true monstrosities that somehow made more sense than the Vertexes ever could.

Her guns danced, reloading and bursting flowers of light from the muzzles as her eyes tracked her next target.

It seemed her weapons were effective against the Strays. Issei said that he needed to land half a dozen blows to incapacitate one with the size thrice bigger than a minibus, but Tougou discovered no difference whatsoever.

Probably, Tougou assessed her surroundings before dismissing the pistols and summoning her sniper rifle. A Hero's weapon possesses an exorcising attribute.

The Shinju granted chosen children with the power to protect the world. As a Hero, that meant Tougou carried a part of the Shinju's enormous power within her and it was expressed through the Hero System.

"In that case…" Tougou hardened the cloths supporting her body and fired at a shadow lurking deep within the entangled vines. "Shinju-sama's divine power must be a lethal poison for these monsters."

It made sense, and the argument held some water better than a deadly Virus that evolved so much it became an eldritch abomination.

However, something was strange.

If Strays were weak against Shinju's divinity… How could the Vertexes withstand, even regenerate themselves back to their original form despite being monsters as well?

As Tougou took in air to calm her nerves, one of her Fairies suddenly appeared and brought up her terminal. Huh…?

"What is," Tougou stopped speaking midway through and whipped her head to a certain direction. "The Vertex is approaching…?"

Why? What had happened? What was going on? Could it be…!?

In the next moment, the Shinju glowed and wisps of light throughout the Jukai congregated to one place.

A sound akin to shattering glass resounded. Tougou sucked in air as her eyes captured a blooming cherry blossom flower in the starless sky. A name crossed her mind.

"Yuuna… chan…?"

What did he just see?

He didn't know, so Issei searched for a way to describe it. With a hand holding his injured right arm, the boy stood up and focused on his vision, relying on the draconic sense he had acquired after sacrificing most of his humanity.

He didn't know why everything went quiet for a moment. Something must have happened, but then something else happened and he was drawn by the scene unfolding in front of him.

"That's…" Issei looked up as flower petals floated down. "Yuuna-chan…?"

An illusion of a flower bloomed in the dark heaven. Light and warmth basked his body, reinvigorating him as he unknowingly took steps toward the source of the mirage.

Clad in white dress painted with shades of light pink, a girl slowly opened her eyes, her dazzling red eyes reflecting a brighter coloration and light. Her ponytail fluttered in the breezes, the dress resembling a heavily-customized kimono with versatility and style heavily taken in account for swayed as a pair of enormous weapons moved behind her.

His breaths stolen away, the boy trembled, looked down and then raised his head.

"…Ddraig," Issei called out. "Do you think I can still do something?"

[What do you think?] The dragon shot back. [I'm in no position to do anything. It's all up to you, so just make sure you won't regret what you choose.]

I see, the boy thought with a nod. That makes sense, I guess.

[Well, maybe you should brace yourself since that gunslinger isn't going to take your decision as anything other than a flimsy excuse.]

"Agh. That's… yeah. I'll be ready for seppuku when the time comes."

[Good. You can't play around with women or even their feelings, after all.]

The dragon sure sounded as if he was reminiscing about a distant memory… Was this a form of escapism too? Issei tilted his head but decided that enough was enough and slapped both of his cheeks.

Issei sharpened his gaze as a flash of red enveloped his body. "We're going to win this, together with everyone."

What happened?

Yuuna felt power coursing throughout her being. It was overflowing and her heart raced as warmth enveloped her. She realized her right arm could be used again and she raised it slightly above her chest.

What followed was something enormous coming into view. A limb was there, but not hers. It was made up from bands of hollow rings with a giant hand made from some kind of metallic material encased by pinkish white armor.

Yuuna instinctively knew that the thing was her weapon. It would move as she wanted it. What did this mean? Something within her whispered the answer and she lifted her chin, removing her gaze away from the armor decorating her body and the white kimono that fluttered alongside her hair.

"…This is… Mankai." Yuuna clenched her hand as the gigantic limb mimicked her action like a mechanical arm.

The white cow Fairy appeared from the left corner of her vision. Gyuuki floated, her four wings flapped with a look as if it was ready for battle.

Mankai was a power given to the Heroes in dire moments The accumulation of battle experience was relayed to the Shinju which hosted a tremendous amount of conceptual records from the Old Era. From that place, the Shinju would draw the necessary strength that could assist the Heroes in battles.

In other words, Mankai was the Trump Card among all Trump Cards.

"…Alright." Yuuna looked ahead at the last Vertex. "Let's go, Gyuuki!"

As soon as she said the word and moved her legs, the world distorted in Yuuna's eyes. In seconds she crossed through the distance as something akin to bursting air cracked behind her, and she reached the Vertex in a flash as it turned around to face her.

Slow, Yuuna realized as the bladed appendage behind the monster flew toward her. I can see it!

Swinging her right arm from below, her gigantic fist broke the bladed appendage with an uppercut. The sharp stinger was crushed into pieces, the appendage torn apart and Yuuna dived in as the Vertex started firing spheres of flame and water.

The girl avoided the barrage as if they were nothing. Her movement was sharper, cleaner, and quicker than before that Yuuna couldn't believe she had been fighting a series of battles beforehand.

With her newfound power, she could fight against her enemy on an even field. No, I can defeat it!

If so… there is only one path she could take.

"Hero…!" Yuuna pulled her right arm in and formed a knuckle. "Puuuuunnccch!"

The blow struck the Vertex – and most of its body vanished within an enormous explosion that scattered a storm of light pink flower petals.

The wind ripped apart, and the Jukai shook as the mighty blow created an aftershock strong enough to disturb the calm sea surrounding the island of Shikoku. Waves crashed and broke apart as petals of cherry blossom flowers danced around Yuuna.

"One more time!" The girl pulled her left arm in and clenched her hand.

At the same time, the Vertex howled. The magnitude of its 'voice' made Yuuna falter but she continued to build up her strength and flew toward the retreating monster.

She was too fast for the Vertex. She was much stronger than the enemy who had caused so much sufferings to her friends. And so…

"Yaaaaaaaahhh!"

As she yelled, Yuuna's fist connected with a curtain of fire that suddenly expanded before the Vertex. Its sudden appearance surprised her, but she refused to accept defeat and pressed on.

Something cracked. Where was it? What was that sound? Did it come from her, or did it come from her enemy? Had she reached her limits already?

…And what of it!?

The now pink-haired girl exerted all of her strength. An overflowing well of power resided within her body right now, so no matter what happened, she could fight indefinitely to ensure the safety of her beloved ones. If one time isn't enough, then…!

"Hero Club's Tenet number two…!" Yuuna pounded a second hit and the curtain of fire began to shed a tiny crack. "Try not… to give up…!"

At the third hit, the cracks expanded but it wasn't nearly enough as something struck Yuuna from the back and left side.

Gyuuki appeared close to her, shielding her from rings of fire and smoke that clouded her vision. The girl understood what that meant but continued to look of her.

"Hero Club's Tenet number five…!" Yuuna smashed the curtain for the fourth and fifth time, the cracks covering most of the wall that blocked her from striking her enemy. "You're likely to succeed…!"

Swinging her left arm, the armored fist flew in.

"If you try!"

The wall of flame shattered into tiny shards. Beyond it, the Vertex had regenerated most of its body but the opportunity had finally arrived for Yuuna.

However, she heard a roaring flame and saw flickering shadows. In front of her, the Vertex was sending out lumps of fire upward. What was it doing?

The girl looked up – and she met the glare of a falling star made from molten lava.

Her eyes widened. She knew that attack well. That was what had hurt her friend. She had to evade, but the extent of damages it had done meant if she did avoid it, the Jukai would be severely damaged and more casualties might appear.

What should I do—

A yellow blur flashed and struck the falling star. An enormous sword tore the air, producing winds as it halted the descent of the solar sphere with its wide body. Yuuna recognized the person wielding such weapon but to stop the strongest attack of the Vertex could only mean…!

"Don't stop moving, Yuuna!" Fuu yelled as her great sword gradually pushed the burning sphere and cut it apart in halves.

At the same time, green threads filled the sky and rained down on the giant abomination.

The Vertex was restricted in place by the glowing green threads. Thousands of them reached out from the forest of trees, taking roots by wrapping themselves around the vines as they chained the Vertex over and over.

Yuuna looked back as she found the figure of her underclassman – clad in white and green dress as threads extended out from a golden ring that hovered behind her.

"Yuuna-san!" Itsuki's voice traveled across the land as the enemy was sliced and diced that only a small part of it was left floating in the air. "Do it! Defeat that thing!"

It took only a moment for her to decide. Yuuna gathered her strength in her fist and dashed forward.

"Don't leave me out of this!" Then from below, a diagram for the Sealing Ritual appeared as a girl clad in red looked up while kneeling at one knee. "Get going, Yuuna!"

Flower petals shrouded the Vertex. As the Corrosion began, the form of a gigantic reversed pyramid emerged far above the imprisoned Vertex.

Yuuna lost the chance to breathe. The Mitama manifested in full view, but… It was overwhelming.

The sheer size. The scale of the thing was downright massive, probably scaling all the way to a few thousand meters. The tetrahedron-shaped soul of the Vertex floated high above the sky but if it were to fall, then the island of Shikoku would be devastated.

The worst thing was that it was floating so high up that Yuuna could safely say it was right on the orbit, maybe somewhere around the altitude a satellite would be placed at.

"Are you kidding me…?" Fuu muttered. "What the hell are we supposed to do against something like that…!?"

What had to be done? What were they supposed to do? What could they do against something as ridiculous as that? Yuuna looked up, and…

"It's still a Mitama," she said. "The shape isn't different and it can't be anything more than the one from before."

"But it's way too high to reach!" Fuu shouted.

"Then we'll find a way to reach it! I'm sure there must be something—"

"Maybe I can help with that?"

Yuuna and Fuu stilled, and both of them turned around to meet the smile of a boy in red armor and a cape.

"Yo," Issei greeted with a wave. "Don't just exclude me without a reason. I'm still here, right?"

"I-Ise-senpai…!? No, wait, but your wounds…!"

The boy shrugged. "I'll bear with it. But more importantly – we still have a soul to crush and time's running out."

He looked at Fuu and bowed his head a little. Fuu blinked, but otherwise looked away with a sigh and a scowl.

"Alright, fine. What are we going to do?" The blonde asked after scratching her head. "None of us are equipped with something like a mass driver, Issei. And your boosters must have a limit of usage, too."

As the boy hummed in thought, he put a hand on his chin and closed his eyes.

"…There's still one way left." Issei's smile turned apologetic somehow. "But it's a little reckless. Want to hear it?"

"I swear, you're insane and I've gone insane too for agreeing with this." Fuu exhaled a long one and raised her enlarged great sword to the side. "I'm not taking any responsibility if anything happened, alright?"

"Yeah, well, it's not a risky plan otherwise."

Issei beamed and his senior glared at him as if trying to burn him into ashes. However, she decided to stop chitchatting and readied a stance.

"Are both of you ready for this, then?"

Issei glanced at his friend. Yuuna nodded, her hand clasping Issei's and he nodded in confirmation. Fuu took that as the cue and raised her sword.

"RraaaaaaaAAAAAAAAAHHH!"

And then she swung her sword with all of her strength toward Issei and Yuuna. The flat side of the blade fast approached, but the two rushed forward at it only to spin in midair and landed their feet on the sword.

Fuu grunted, but she didn't stop swinging. Issei felt the winds becoming a wall, jarring a few parts inside of him because of the pressure bearing down on him. Even so, he endured as he kept a clear view of the sky that was obstructed by the Mitama.

In the next moment, both he and Yuuna were launched straight to the sky.

"Ise-senpai!" Yuuna shouted.

"Got it! Don't let go of my hand, Yuuna-chan!"

He activated the keyword and Boosted Gear strengthened his body. He felt the rest of his stamina greatly depleting, almost hitting rock-bottom, yet he couldn't stop there. If I can't make it in time, then…!

"Ddraig!"

[I'm all set! Say the words, partner!]

The boy grinned and inhaled.

"Shine – Overboost!"

Red flooded her vision.

The hand she held became rough and scaly like touching the scales of a lizard. Even so, Yuuna found warmth in the touch and she captured the image of her friend whose armor transformed to cover his entire body.

The boy's image was soon replaced with an image of a small humanoid dragon. The armor he donned was bulky, possessing so many sharp edges and held an imposing impression that Yuuna couldn't help but be a little scared of what lurked beneath the green eye glaring from the headgear.

But it's fine, she thought, reassuring herself no matter how much she feared for the future. It's fine to be afraid. Just… don't let him go, no matter what.

She was painfully aware of the boy's decision. Even as the two reached the Mitama, her thoughts swirled around and she wondered if she could have done something that could have prevented this.

However, Yuuna realized that she couldn't do everything on her own.

"…There it is," said her friend. "I only have one shot left. The rest is up to you, Yuuna-chan."

"Un…" The girl nodded, sweeping aside her idle thoughts and focused on the task at hands. "I… Thank you, Ise-senpai."

For so many things. There might have been nothing she could do to repay the boy's kindness, but Yuuna could at least try to help even if it amounted so little for him.

For some reasons, however, Issei laughed unabashedly. Why is he laughing…?

"Yuuna-chan."

"…Yes?"

"I'm glad that I met you."

…Huh? Yuuna blinked, her mouth agape but Issei already let her hand go and rocketed straight toward the Mitama.

"Ah…!?" The girl yelped as she felt something passed over and shrouded her body. "What is…"

Something was different. Something had changed. She felt as if her stamina was replenished and she could take on the world by her own. A sense of liberation breathed into her chest, filling her with pure, unblemished power.

It can't be, she thought. This is Ise-senpai's doing…?

How? Why? Since when? But, if he could help by empowering her, then…

"I won't let it go to waste!"

Gravity began pulling her in but her friend moved even faster than she ever could. She was literally beaten in terms of speed by Issei, and a red aura suddenly burst out from his body.

Before the two, the black lines decorating the titanic tetrahedron glowed. An instance passed and it moved as if reacting upon the approaching Hero and Dragon.

What followed first was the sudden removal of parts of the materials making up the Mitama. The reversed pyramid launched smaller cubes, each of them fired at the speed of sound toward Yuuna and Issei.

However, the barrage of attacks was crushed by the boy. When the cubes touched his aura, they dissolved into tiny particles that were further erased into nothingness.

Hyoudou Issei roared as he plunged into the Mitama.

Destruction spread across the flat surface of the tetrahedron. Dirt and wind ascended as pillars of chaos ravaged the surface area of the core of the Vertex. However, the damage wasn't enough as swarms of cubes flew and showered the place the boy was at.

It was overwhelming him. There was no way Issei could endure against millions of bullets-

"Yuuna-chan, don't stop moving!"

Yuuna blinked before a few rays of blue light crossed the heaven.

Once, twice, thrice… The beams seared through the cubes and disrupted the flow of the Mitama's attacks. Yuuna knew those azure lights. They were all bullets shot by one of her best friends and fellow Hero.

"It's okay," Tougou's voice rang in her ears once more after a near-transparent screen peeked out from the corner of her vision. "Everyone will return alive, so please…!"

Another ray of light blasted the cubes that endlessly attacked the red dragon as he tore into the tetrahedron with his bare hands. At the same time, she saw green vines of light reaching and cutting down any fallen cubes that might hit the surface.

"Defeat that Vertex...!"

Explosions scattered, chunks of debris spread alongside rolling chunks of dirt. The noise was unbearable and it was difficult to recognize whether Yuuna's arms were trembling due to the shockwave or because of her uncertainty.

Within the unrecognizable mess that was her target, however, she spotted a gaping pitch-black maw and immediately steeled herself.

"Leave it to me, Tougou-san!"

Without hesitation, the girl dived down like a meteor. She tried her very best to ignore the battered form of the boy clad in red armor, or even the small cubes that began to rain down upon the surface of Shikoku.

She gave her friends her trust and she reached the Mitama as fast as she could. With the additional boost in her speed, she flew into the dark path forged for her. Nothing opposed her way. The Mitama had redirected all of its attention to different targets and she soon arrived at what appeared to be a wall drawn with black lines.

So it still has some tricks under its sleeves…! Yuuna gritted her teeth. The cacophony of battle echoed from right behind her, but she acknowledged her duty and did what she had to—

"OooooooooOOOOOHHHH!"

Swinging her arms, the armored mechanical fists struck and pulverized the wall blocking her way. But there were still more so Yuuna repeated the process by punching her way through, again and again and again.

Not even once did she take a break. The girl hammered a path forward with her fists as the Mitama cracked and crumbled from within. Every layer of protection was demolished, every wall was smashed through no matter how hard they were.

Regardless of the increasing pain and the throbbing of her wounds, Yuuna continued to press on. She felt as if time had stood still and a part of her wondered how many walls she needed to break through.

Even so…

"Aaaaaaaaaahhh!"

Even so, she held on to hope and struck the darkness for one last time.

Glowing cracks emerged alongside sounds of destruction. Yuuna's eyes widened as the darkness crumbled and gave ways to a hollow space with a glowing sphere floating in the middle of it.

That was it. She reached her destination. She had reached the innermost of the Mitama, and she was sure that the source that made her friends to suffer was right before her eyes.

The town, the people who live in this land, everyone's daily lives and the world's future…!

"We will…!" Yuuna raised her right arm and swung her fist. "Protect them, allllllllllllll!"

The Mitama shattered – and everything turned white.