A black hole is made up of densely-packed mass that causes space to bend. The general consensus was that it wasn't considered a state of matter, but simply a mass.
Imaginary mass works just like normal mass. It imbues more 'mass' (to not be confused with weight) to its target. The point of the target's tolerance limit being exceeded by the actual imaginary mass was the time it starts turning akin to an exploding star.
Once something reaches the event horizon (i.e., the central area of the black hole), that something reaches the point of no return. Their fate was to get crushed by the overwhelming mass in all directions.
Sou-!
Kurumi squinted her eyes as she saw a silhouette barely escaping the black hole's range. A closer look made it evident it was the Herrscher.
"He escaped..!"
Yoshino came to her side. Along with her was the huge rabbit who carried the MANTIS in its mouth.
"Ideal fluid… It's not surprising."
Kurumi knew the Herrscher of Wind had something that could let him escape a miniature black hole.
Ideal fluid.
It was a hypothetical substance merely used in hypothetical scenarios. It was the equivalent of the neglected air resistance on typical projectile motions.
In simpler terms, ideal fluids aren't affected by pressure, do not have friction, and flow at a constant rate. It was a substance that defies the rules of physics itself. Its existence was only to understand certain problems better. It does not exist in the real world.
The Herrscher of the Wind's power made such a thing appear.
While Kurumi was thinking of counter plans, the Herrscher was also calming himself.
"A literal black hole… The others wouldn't stand a chance against it… would they?"
He was aware that among the four of them, only the Herrscher of Thunder stood a chance at escaping a black hole.
From the moment Kurumi's "power" was exposed, the Sixth Herrscher gave them a heads up. They planned for two months just to circumvent it—to return to Earth and launch a smooth attack.
Aside from that…
"...No. She would know by now."
He thought of the 'menace' they painstakingly tried to avoid.
For humanity, he was the strongest hero.
For the honkai, he was the strongest foe.
Thinking about the Sixth's unusual behavior towards Aleph, he grew more confused.
'Why does she want to play around like this? His close friends aren't as strong as him…'
Just like how Ling grew confused at the Cocoon's behavior, the Fourth had the exact same sentiment towards Ling—a cycle of irony.
'The ideal fluid serves as the best barrier against her.'
Ideal fluids are incompressible and aren't affected by shear stresses. As long as it was present around the Fourth Herrscher, black holes wouldn't do anything to him… so long as he does not enter the unpredictable event horizon.
Even light gets trapped inside it, more so if it was only him.
'Be aware of her unusual attacks.'
Sou-!
As he thought, a rain of thick hailstorm struck him down. It was evident Yoshino made a move.
Swoosh-!
Bam-!
The hail storms were sucked by a cyclone and were sent all over the place. Each one of them crashing down was equivalent to a small-sized mortar shell.
Just as the Fourth Herrscher thought there was another upcoming attack, he saw a phantom of a clock. Kurumi's musket was pointed to the two-o-clock sign.
"Bet."
Bang-!
The sound of the bullet inadvertently made him move. He did not look at the bullet and based it on the soundwaves instead.
Little did he know…
Pshk-!
'What..!'
…it was his fatal mistake.
It was unknown when, but a flintlock pistol appeared on her left hand. The Fourth Herrscher could swear he did not see it until now.
'I…'
He was surprised to find everything remained the same. He did not suffer any tangible injuries. However, he soon noticed an unnerving fact.
'When did she become so fast?!' He began to correct his thoughts, 'No, I am moving slower..!'
This moment of delay allowed Kurumi to draw closer to him. Their distance of fifty meters was rapidly closed in seconds.
The Fourth Herrscher's speed was drastically reduced by her Second Bullet, Bet. Time itself ran slower by half on him.
By the time he could recompose himself, Kurumi fired the second volley of bullets. This time, both the flintlock pistol and the musket pointed towards seven-o-clock.
The Fourth Herrscher only had enough time to use the combination of ideal fluids and his control of the wind to propel himself upward.
Sou-!
Psshk.
The bullet barely scraped his right foot. Swiftly, the Fourth Herrscher 'froze' midair. That served as the signal to do things.
Buzz-!
Like an ink on a pure white paper, frost emerged from a small dot and rapidly extended to the entire institute's radius. Beside the mechs and the sole building that housed Einstein and the rest, everything became covered in frost. A strong blizzard was created out of thin air.
'I see it.'
In Kurumi's sight, several ratio lines appeared. It was the second 'chance' Aleph gave to her—Ratio.
She was about to launch a newly-made devastating attack—one that surpassed her twelve bullets—when someone appeared out of thin air. Her eyes widened upon the realization of who it was.
Crack-!
Shatter-!
A slender white finger touched the back of the Fourth Herrscher's head. His frozen time was immediately removed.
When the latter turned around and looked who it was, complex emotions appeared in his eyes.
"Why…"
Seemingly knowing his question, the "someone" spoke.
"You were sent to your death."
Aleph's cold words froze the Fourth Herrscher.
"Ironically… your indiscriminate hatred sent you to your death."
"...Why..? Sister Ling was confident you would not appear…"
Aleph did not answer his question.
"I will meet with her later. For now…"
The Fourth Herrscher looked directly at his eyes.
At that instant, what he saw was no longer limited to Aleph's pair of golden pupils. Complex information began filling his mind.
Aleph's "true form", which abstractly consisted of a black and white dragon tainted with an indescribable light; an endless void filled with divided lines and bent space; and a black spot that rendered everything meaningless, directly affected the material world.
Boom-!
Bam-!
The shattered soil caved in deeper before it was covered by a green prairie. His phenomena storage acted on its own just by showing his "true form".
Half of his ten-kilometer radius was changed to a prairie, while the remaining half retained its caved soil. The entirety of the five-kilometer radius was filled with a background akin to space's. The sense of incongruency formed by them made it evident they should not exist in this world.
By the time these changes stopped…
Bam-!
Splatter-!
…the Fourth Herrscher's body exploded into a bloody mess, leaving nothing but a bloodied green rhombus crystal in Aleph's hands.