*
"..." (Hikari)
Words quickly lose meaning. It didn't even have to specify this situation, a battle for the life and death for whole species. Over time, words become obsolete and new ones take its place. It is a natural process, the new always replaces old.
In an instant, the Demon King recovers his lost leg and all the gaps in its armour mends together like a living thing healing its wounds. As if the heavy metallic platy armour was a slime, it rapidly transitioned between solid and liquid, covering its holes and hardening. Fighting here would be fine as well, if magic resources are directed towards the main body here, the clones fighting outside would be reduced in power.
"fuuh~, stop thinking you're all high and mighty. Even if it gives me a bit of an edge, it's pissing me off." (Kaede)
Drawing from the experience of fighting in every battle, she successfully predicted most of the Demon King's attacks and dodged them. It was evident in the different forms of injuries both had received. She carefully planned out her own attack while avoiding the enemies, catching Hikari in a surprise and managed get a limb out of it. On the other hand, Hikari simply kept overwhelming her with attacks, giving her no time to think.
It was precisely due to the experience that she's gotten that she could fend off this high stress situation and constant barrage of attacks while making up her own plans. Even her injuries reflect. She sacrifice her flesh and blood, receiving numerous surface level wounds. But she didn't receive anything too deep or substantial. As an A grade magical girl, surface wounds heal absurdly easily.
The enemy's aura linger in their attacks, they act similarly to the time space distortions that Yiren leaves with his sword. Simply using one's aura, one can plug up their opponent's wound and prevent it from healing. It was evident from how the more magic one used, the slower the enemy healed. It wasn't simply due to the sheer quantity of damage that slows down a person's regeneration, it was also the quantity of magic, causing a multiplicative effect.
That's why higher grade beings can kill lower grade beings easily, but the closer the gap in power, the more drawn out the fight. There eventually comes an equilibrium where the wounds don't heal too fast or too slow, so if 2 equally powered beings fought, it might take forever to end. Well, that's not the case here though. Hikari was an entire grade above her, she's faring well but only by the skin of her teeth. A small slip up is enough for her to lose, a true tightrope fight.
To put this into perspective... Every wound she had received so far was from the Demon King missing his attack. None of them landed. She can't let him rest for long, or the clones might recover their strength. Forcing him to spend his magic here is the most effective way to aid the war... But obviously, the most optimal way is to kill the Demon King.
Using Last pace, she vanished from his line of sight with a side step and threw her rapier. Using a frontal attack is too predictable, but it can still be incorporated with a mixing of attack patterns. There's no need to limit herself here. She vanished from her new spot just as he found her, dodging the flying rapier which scraped his neck in the process. She launched a kick just as the rapier was dodged, smashing her heel into his armoured jaw and turning his face up.
The difficulty isn't anything too complicated. In fact, the Demon King's attacks are super simplistic. The difficulty comes with the simplicity... His attacks are straight forward but insanely strong. He could compete with any S grade magical girl one on one. After many battles, gauging the enemy and predicting the danger had become a second nature, as if she developed a new sensory organ. A mere intuition that she listens to, to live.
Bending her wrist to position her rapier vertically, she steps to the side where Hikari's great sword barely misses her cheek, even her rapier was necessary to reduce damage from the shock waves that came as a result, the overwhelming force of his magic and strength rips the air and everything else in it apart. If they were outside the castle, it would have no doubt left a large ravine in the ground, followed by a simultaneous earthquake.
The impact of the shock wave crushes her legs, like a mountain was dropped onto it. Her muscles numb around her bones, the recoil of the attack is all directed into her heels as the castle was indestructible. This was an attack that barely missed. The further she dodges from an attack, the lighter the burden on her body. She jumps up with Last Pace, firing void spears in all directions.
One of the spears cleaves into the edge of his upper arm armour, manipulating the gradients, Kaede sends her aura and random debris around into the wound, preventing its quick regeneration.
Her body vanishes from the Demon King's sight with Last pace, throwing a frontal assault with a wide but tight slash, followed by a quick successive dodge. She can try to shorten the intervals between Last pace leaps as much as possible by continuously employing it, the risk being that if Hikari accurately predicts the destination of a leap and attacks it, she wouldn't be able to defend. But this was a necessary risk, in order for her not to be eliminated instantly.
If she holds on a little longer, one of the Arc Maidens might arrive victorious from their battle to help out. At present... She simply has not enough strength. Last Pace increases her Strength and Speed to S grade, a quantity of around 43 million since the threshold for S grade qualification was 1 million.
Hikari swiftly heals her wounds, the debris and aura that Kaede tried to cause an inflammation with were easily ejected out in less than a second. With their perception of time, a second has already become quite a long time, but to a normal human they wouldn't be able to see anything happening. They were travelling at absurdly fast speeds that the air pressure generated could easily kill a city of humans.
As the castle was indestructible, it was acting as a canister containing the high pressure high heat environment, with Karell's spatial magic acting as a cap to block off the corridor. But if it was them... The heroes shouldn't be so feeble. If she held on a little longer, they might be able to recover in time to rejoin the fight. Then her job was now clearer. She wasn't a hero at all, she's a king candidate. A leader in the field, but not the spearhead.
Her body had adapted to the pressure and the heat as she was one of its generators, it was a hellish environment that could kill a weaker magical girl. But... Yeah, she should do it. This was now her domain. Using her first skill, she gathered all the what pressure in the room into the shape of a spear and back stepped. The Demon King was intelligent, he wouldn't just let her do as she pleased.
She exploited the hellish environment, gathering that hell into a single rod shape and enhanced it with her magic. She had to follow it up with a swift dodging of the next attack, but since she back stepped, the opponent's attack will still affect her to a large degree. The air pressure struck her head on while all her magic and focus was concentrated onto the newly forged spear of hell. It was a unique structure only possible because 2 S grade powers affected an indestructible environment and continuously accumulated heat and pressure to such a degree.
Just as the air pressure struck her, she pulled the spear back which hit the Demon King, he stood between her and the spear likely thinking that it was too dangerous for Kaede to launch the spear at herself. It was a well placed bomb, in the middle of the room with endless possibility of freely changing trajectories. The spear converged into a single point in Hikari's bag before erupting. Blinding light engulfs the room like an all encompassing flash, burning the retinas of those who are unprotected.
Kaede covers her eyes as it collides, she formed a vacuum shield around herself to divert most of the energy. When the light died down a few seconds later, there was a large gaping hole in the Demon King's torso.
"... Hollow?" (Kaede)
"..." (Hikari)
A hollow armour species... There were many classes of monsters, way too many to list them. But to simplify it, there is the general semi natural abomination of the wild, organic and inorganic matter fused with spontaneously forming magic circuits into amalgamations of its individual parts. A bird's corpse would cause a monster to have bird parts, a cat's corpse would cause it to have strong quadrupedal limbs or slick sharp claws.
Then there is the main topic of this revelation. Semi-unnatural (magic) , quarter-natural (armour) , quarter-fantasy (living). It seems that not only Yiren, but the Demon King was part of this category. To be made up of a monster and a fairytale, ascending themselves into a higher being as the world itself gives them the power to fulfill the fantasy... To be clear, it is the world that is fulfilling a fantasy, and these existences are just byproducts of it.
This nature of his explains how the armour was able to regenerate that fast, how he was moving so swiftly and lightly despite wearing all that armour, and... Why the large gap in the Demon King's torso has no blood or hint of a body inside. Hollow living armour, it's safe to say the Demon King is an ascended form of this fantasy creature.
"Ofuh~" (Kaede)
The edges of her lips stretch back as if their initial rigid structure cracked and reforged into a smile. The ridge of her nose wrinkled as her eyebrows inched closer and her eyes widened laying their clear sights upon her enemy. All of the pressure and heat had been spent, but knowing the Demon King's species was a lot of useful information. So their king might be elated based on strength, then he wasn't some invincible being after all. He was just another demon, a slightly stronger and more intelligent demon.
Her heart beat rose as she places the tips of her fingers on the ground. Using Last pace, her vision fades away into a blur, returning right away to the top view of the room. She leaped far into the air and summoned her magic, pumping loads of her magical particles into a single attack. Black surges of void imitating electricity surround her body and gathered into a single point, an orb orbiting around her right fist. Her right arm is outstretched and pointing at the enemy.
Hikari vanishes, brandishing his superior speed. Before that, she fires her attack at the back of her own head. Hikari's gauntlet reappears in a knife hand shape, approaching the back of Hikari's head at an unobservable velocity. Since Hikari was moving faster, her arm reached Kaori's head first despite attacking after Kaori fired the attack at herself. Timing it just right, her magic burst forth like a black laser beam, swallowing the gauntlet in the process.
Next, Kaede pressed against the ceiling and used Last pace to change location multiple times, the Demon King followed closely each time as she chased after her. Mirages of light purple and black chase one another in this thoroughly sterilised throne room. Eventually, Kaede jumps against the previous laser beam she shot off. It wasn't wasted, it didn't vanish into magical particles right after taking a single arm. She allowed it to orbit the room so the energy could be recycled.
This time she jumped at the black laser beam head on, it phases through her and strikes the heart of the Demon King following closely behind. The impact smashed his armoured body against the floor, equally distributing it's energy throughout his body to completely batter him.
She lands on the ground at a short distance away, catching her breath as she watched his collapsed body. She was cautious, there was absolutely no way that meagre attack could finish him off. It was an aberrant faith for one's enemy, trusting their strength and her own estimate of their strength. Sure enough, he gave up on the feint and casually returned back up. He stood on his ground with a menacing aura that crushed everything around him.
Allowing one's aura to flow freely is akin to a war cry. But she would fall for it. She prepared another attack. Charging up one's attacks with more fuel was inconsistent, if she packed in a particularly large amount and it failed to take out the enemy, she would just be sealing her fate.
"Fine. Fully Retained Magia." (Kaede)