"Boom!" The ape shot out a beam from its mouth, just like the previous ape, to Kai. It looked like the ape hit him.

Ayaka couldn't ascertain Kai's condition as the smoke prevented her from doing so, but judging from their positions, he should've gotten hit by that explosion.

Ayaka opened her mouth wide. She thought, 'Why is he the one getting hit? I should be the one getting hit. He's always helping me again and again. If I were the one who got hit by the ape and if he were still alive, he would've had a way to kill this ape.'

Blood inside her head started boiling again despite the numerous times Kai told her to calm down. She made a magic circle out of rage.

"Scarlet Explosion!"

She used that enormous explosion again on the ape.

"Boom!"

It was a direct hit to the ape. But because she was too close to the explosion. She got blown away by the shockwave made from it.

She crashed into a tree again and spat some blood. She tried to look at the explosion.

'Did I get him?' She couldn't see it as the smoke was still rising.

"Roar!"

Suddenly, a thunderous roar filled the air. The ape blew the smoke away. One of the ape's hands was charred black while there were also a few black spots on its body. It seemed that the ape sacrificed one of its arms to block the explosion.

"Kh!" Ayaka gritted her teeth. She couldn't move her body, and the ape was staring at her angrily.

"Ding!" But before the ape could charge toward her, a high-pitched sound suddenly echoed from Kai's position.

Behind the smoke, Kai was using his Melody Resonance to produce this sound. But this time, he didn't use it to affect their brainwaves, he just wanted to let all of them notice him.

"Roar! Roar! Roar!" Numerous roars were heard from the forest.

Kai smiled as he leaned his back on the tree. His hand was broken when he used it to block the ape's punch. But at the last second, he managed to use his improved shield to block that beam-like attack.

The energy scraped away the power from the beam and its explosion. It destroyed his barrier but didn't do any significant damage to him.

But he was so lucky to be alive. Kai struggled to get on his feet when he heard lots of magical beasts starting to head their way.

"Roar!" The ape roared at him.

Kai only smiled at the ape and said, "Come."

The ape then ran toward him. He threw a fist on Kai's battered body.

Kai gritted his teeth while enduring the pain. Because Ayaka had injured its entire left hand, the ape was forced to throw its right hand to attack Kai. But he used this as a chance to dodge its attack.

He jumped toward the ape's left hand. Because the ape couldn't do a 360-degree turn after he attacked Kai's with its right hand, Kai managed to avoid the worst.

Kai immediately ran toward Ayaka. But suddenly, the ape roared and chased after him.

"Kai!"

"Ayaka, use your fire net!"

Ayaka's eyes flashed. She knew what he wanted to do. After finding that Kai was alive, she somehow got extra energy in her body. She tried to move her hand and raised it toward the ape. A magic circle appeared again.

"Fire Net!"

A fire net akin to the previous one suddenly appeared once again between Kai and the ape. It blocked the ape from catching up with Kai.

The fire net started burning the ape.

"Roar!" It screamed out of the pain.

Kai immediately helped her. He pulled her out so she could stand. She managed to stand up, but she had to lean on a tree so she could continue using her fire net.

Kai suddenly put his noise-canceling headphones on Ayaka.

"You?" Ayaka was confused by his action. But she suddenly realized that she couldn't hear anything. This proved how strong Kai's noise-canceling headphones were.

Kai only opened one of her ears. He said, "Do you remember how I told you that I have a skill that will also hurt me when I used it? It's time to use it. If we die just like this, our score will be low. Just lean back on this tree and watch."

Kai smiled and put the headphones back. He made a Sound Insulation Room around her and came outside the room. He only smiled at her, but this smile only made Ayaka even more worried.

Kai suddenly made a huge green magic circle. He also made two small magic circles around his ears.

"I really hate doing this." Kai sighed. He looked at the struggling ape that was trying to break Ayaka's fire net. He also heard the sound of monsters that were coming to this place.

(AN: dB or decibel is a unit used to measure the intensity of a sound.)

"It was said that occupational exposure to ultrasound in excess of 120 dB may lead to hearing loss, occupational exposure to ultrasound in excess of 155 dB may produce heating effects that are harmful to the human body, and occupational exposure to ultrasound in excess of 180 dB may lead to death.

"Let's raise the bar a little bit more, all right. 200 dB is enough to lead even magical beasts to death." Kai said.

He had tested something like this with so many cautions. But the most important thing was that he tested it in a practical tube like this. He sometimes used his sister's influence to use a practical tube so he could research his skills like this.

This was the last card that he would use when fighting magical beasts. He had died countless times when was researching this skill just to understand how to make a skill that could produce a very 'loud' sound.

The biggest reason why this was his trump card was that he would most likely die if he were to use this.

He might be able to use it inside the Sound Insulation Room, but he didn't know why, but when he used it inside the Sound Insulation Room, it would break far easier than when he was outside. That was why he left the room and let Ayaka stay safely inside.

Kai waited a little bit more so more and more magical beasts would come to this place.

In a span of three seconds, he could see numerous magical beasts approaching him. If he didn't use his magic at this point, he would die before he could use it.

He immediately clapped his hand and activated the magic circle.

"Ultrasonic Assassin."

"Ding!"

A very loud noise suddenly echoed through the entire forest.

"Roar! Roar! Roar!" The beasts were roaring because of this sound, especially, the beasts that were close to Kai.

They stopped moving and tried to cover their ears. This sound was killing them.

But the one who took the most damage was Kai and the ape.

When he activated his magic, his eardrums almost burst.

The magic circle on his ears was a small Sound Insulation Room that could protect him for a few seconds. But to kill these monsters, he needed more than those few seconds.

One second...

Two seconds...

Three seconds...

Until finally, at the fifth second, the magic circle on Kai's ears broke. His eardrums immediately burst out, and blood spurted out of his ears.

Blood started coming out of his eyes, nose, and mouth. When he spat some blood, he fell to his knees. It could be said that he already had organ failure because of this sound.

But he gritted his teeth and maintained the magic.

When Ayaka saw this, she didn't know why, but a wrenching pain tore her heart. She wanted to help Kai at this moment, but her body refused to move.

"Move! Why can't you move at this time?" Ayaka couldn't help but let out some tears from her eyes. Kai did this so they could win their bet with Katsuragi Takaki. She was the one who accepted that bet without even consulting him.

"Move!" She screamed, but even so, she couldn't move her body.

Kai was struggling as blood started coming out of his pores. He used his hand to support his body and maintained his magic. Even the Sound Insulation Room he made for Ayaka had started cracking.

Numerous magical beasts in his surroundings started dying one by one.

In the twelfth seconds, Kai suddenly spat blood and fell to the ground lifelessly. He died.

His magic circle and Sound Insulation Room started to disappear. Ayaka knew that Kai finally died. She gritted her teeth and continued to struggle. She saw that the ape hadn't died yet. She needed to at least give that ape the last blow.

The magical beasts that hadn't died yet started to get up. They wanted to ram and kill the dead Kai and Ayaka.

After her continuous struggle, she finally managed to raise her hand. She used her skill toward the ape again. She looked at the ape that was bleeding all over its body.

"Scarlet Explosion!"

"Boom!"

The ape took another hit from Ayaka's explosion.

"Roar!" The ape was still roaring, but its roar was beginning to show signs of weakening.

"Just die already!" She shouted desperately. She couldn't use her magic again at this point.

"Roar! Roar! Roar!"

Out of nowhere, she got hit by a rhinoceros from the side, thus killing her.

Ayaka and Kai finally came back to reality.

They were startled as they looked at each other, but they soon turned their heads to the screen. The screen displayed how many monsters they killed during their stay inside.

S - 0

A - 1

B - 4

C - 36

D - 98

E - 156

F - 237

"..." Kai was speechless. He muttered, "So, after that much effort, we still couldn't kill the ape?"

Ayaka remembered how she had hit the ape with another explosion. She flushed red, and she said while looking away. "The ape was too tenacious."

She then turned to Kai again, and Kai also looked into her eyes. They chuckled.

"Haha... So it was still no use, huh..." Kai laughed while leaning against the wall of the tube.