A moment of silence passed as everyone waited for Isaac's attack to take effect.
Still holding them by their necks, Kaizen slammed Aziel and David into the ground.
"I-I don't understand," Isaac stumbled backward, "not even sever works on him?"
Kaizen turned around and began to plod toward Isaac.
"You still don't understand?" Kaizen asked.
Rosa emerged from a mirror beside Aziel and David.
"If sever doesn't work on him," Rosa said as she helped David and Aziel get on their feet, "then nothing else will."
Once again, Kaizen's question was left unanswered.
"Causality," Kaizen hinted.
Isaac's eyes grew wide as he began to understand what Kaizen was implying.
"Wait," Isaac said, "do you mean-"
"Yes," Kaizen answered, "not only am I above you, but I am above the very concept of causality itself."
"Due to this, simply interacting with me is virtually impossible."
Before Isaac could move, he felt something slam into his abdomen, sending him soaring backward.
"The problem with you humans," Kaizen muttered, "Is that you allow your curiosity to cloud your judgment."
Just before Isaac ran out of momentum, he felt another blow. This time to his back.
"In what world," Kaizen continued, "did you believe that four humans could defeat the most powerful apex devil?"
Isaac tumbled forward before Aziel, David, and Rosa caught him in their arms.
The spirits felt Kaizen's heavy steps growing closer and closer.
"I can reattach us to the flow," Rosa explained, "but due to my diminished spirit and the number of times I used it earlier, I can only pull off attach about three more times."
"Alright," Isaac stumbled to his feet, "you three better get going."
"What are you talking about?" Rosa countered, "I'm not leaving you to die."
"What other choice do we have?" Isaac replied, "He's just toying with us. He could end the battle at any moment. Three of us can escape and, one must stay."
"That one must be me," Isaac continued, "besides, there's no death more honorable than a death for those you love."
"No," Aziel said in a sorrowful tone, "I encouraged David's proposal to fight. I should be the one to stay."
"That's not true," David added, "since I proposed it first, I should be the one to stay."
"It's my fault as the older brother," Aziel argued.
"You're only older by twenty minutes!" David contended.
"Are you two insane?" Rosa asked, "there's no way your father and I would let any of you stay. The only thing to be decided is between your father and me."
The spirits suddenly began to feel Kaizen's dark aura materialize.
"He's getting serious!" Isaac yelled.
The other spirits scrambled to get out of the way but, Isaac stood his ground.
Kaizen's aura had now grown to the point where the spirits could no longer move within it.
They all braced for impact but were met with nothing.
"Wait," David said as he struggled to move. Although he could not see in Kaizen's thick, dark aura, he could sense the others.
He felt Kaizen, the source of the dark aura, dashing toward Isaac.
"He's only aiming for father."
The thunderous explosion that followed gave the spirits and spectators an accurate image of what had happened.
The explosion sent Rosa, David, and Aziel flying in different directions.
Everyone in the area was completely silent as they were in a state of complete and utter shock.
The unbearable silence was broken by Isaac's voice.
"Get out of here!" Isaac shouted.
The spirits snapped out of their state of shock and, the last they heard of Isaac was his booming voice.
"What an honorable way to go!"
Isaac let out an explosive laugh that echoed around hell before his laughter suddenly ceased.
Aziel and David landed on opposite sides of hell. With Kaizen between them.
The attack had sent them to an area outside of Kaizen's aura, allowing them to move freely.
David's dark aura erupted, while Aziel's white aura erupted. The twins both had empty eyes, filled with sorrow and hatred.
"I was useless," David and Aziel unconsciously said in sync.
Beside both Aziel and David, a scythe appeared out of thin air.
David's scythe was entirely black. It had a black blade and an equally dark handle.
Alternatively, Aziel's scythe had a silver blade with an entirely white handle.
"Kanashimi," the twins said in sync, "my ririsu blade."
Kaizen looked around. In front of him stood Rosa, whose eyes were still wide from what she had witnessed.
Just as Kaizen was about to attack, he felt two foreign presences.
To his right was someone engulfed in a white aura. The person was holding onto a white scythe and, the silver blade dragged through the floors of hell.
To his left was another. Engulfed in a black aura, this person was holding onto a dark scythe and, their black blade dug through the floors of hell.
"Ah," Kaizen said, "ririsu. A human's true power. How interesting. The true power of a human grows in the heat of battle."
"David," Rosa said, looking to her right. "Aziel," she said as she turned to her left.
The twins simultaneously dashed at Kaizen.
"Unfortunately," Kaizen whispered, "It's still futile."
Aziel swung his blade to the right, toward the back of Kaizen's neck.
On the other side, David swung his blade to the left, toward the front of Kaizen's neck.
Just before the blades made contact, Kaizen and his aura disappeared.
With nothing between them, the black and white blades clashed, causing another loud explosion that echoed around hell.
Noticing Kaizen's aura reappearing, Aziel instinctively leaped in front of David.
Kaizen appeared with the tip of a black blade sticking out of his palm.
The blade punctured Aziel's left eye and, the attack left a noticeable gray mark on Aziel's transparent spirit.
Aziel let out a terrifying screech before dropping to his knees. His scythe dropped beside him and, Kaizen disappeared once again.
"What was that weapon?" an anguished Aziel asked.
"Aziel!" David shouted as he dropped down to aid his brother.
David noticed Aziel's scythe disappear and, he quickly reacted by standing in front of Aziel, bracing for impact.
Kaizen reappeared in front of David. He coated the butt of Aziel's scythe with his dark prana and, he struck David in the torso.
The sudden surge of power David felt earlier completely disappeared.
He dropped down beside Aziel, feeling too much pain to utter a word.
The attack left an oval hole in David that began just below his neck and ended just above his hips.
Kaizen dropped Aziel's scythe beside the twins and, he pointed his hand toward them.
"Goodbye."
Behind Kaizen, Rosa shook her head and came back to her senses.
"What am I doing," Rosa whispered, "Isaac sacrificed himself for us. I can't let his death be in vain."
Still on her knees, Rosa lifted her arm and manipulated her ririsu prana.
"Ririsu Prana: Attach!"
"The two of you will now be attached to the area beside me!"
Aziel and David appeared beside Rosa.
"Y-you used it," Aziel said, "using attach on both of us means you have only one more use."
"That means only one of us can escape."
"No," Rosa said, "I can pull it off an extra time. It'll cost my life but, either way, I'll die."
"The only problem is, I don't have enough power to send you exactly where your physical body is."
"The best I can do is use attach like a sort of magnet."
"I'll use attach and focus on one focal point somewhere in the flow for each of you. That'll cause your physical body and your spiritual body to be pulled to that point of convergence."
"You'll probably appear in different places so, you'll have to find your way back to the library on your own. Your father and I trust Hashira like a brother. He'll be there for you two."
Kaizen turned around and began to walk toward the spirits.
Rosa lifted the hands of her two sons.
"I love you guys," Rosa said.
Too weak to object, Aziel replied, "I love you, mother."
Still unable to talk, David mouthed the words, "I love you."
"I love you too," Rosa mouthed back.
Still holding onto their hands, Rosa began to manipulate her prana.
"Ririsu Prana: Attach!"
"Your spiritual selves will now be attached to your physical selves!"
Just before the twins disappeared, they saw their mother smile one last time.
Behind her, Kaizen had his hand extended forward, indicating he was about to attack.
The words Kaizen said were quieted by the chants of the spectators.
"All hail Lord Kaizen!" they chanted.
"Kaizen," the twins mouthed in sync.
Right there, Aziel and David learned a name that they'd never forget.
Aziel appeared on a dark planet, now back in his physical body, the wounds he sustained began to heal. However, his eye did not heal, and the gray slash stayed.
David appeared on a bright planet. He could feel the hole in his body healing ever so slightly but, it was evident that the surge of power he felt in hell would not be back for a while.
Unconsciously, the brothers mimicked each other's actions.
Both released a gut-wrenching yell as their auras engulfed the worlds they were on.
David's dark aura engulfed the bright planet he was on, while Aziel's white prana engulfed the dark planet he was on.
Their yells embodied every emotion they felt, grief, sorrow, anger, hatred, and most of all.
Emptiness.