(AN: Telling you again. Correct me if I made mistakes about the concept. But don't forget that this is only a fantasy story.)

"Not good!" Kai crossed his hand while making a green magic circle.

Kai used his improved barrier to block this fist. The magic circle suddenly made a weird sound that Ayaka couldn't decipher.

But it was called an 'improved barrier' not because of the sound. It was because of the energy produced by the sound.

Kai used the concept of oscillation to improve his barrier. He took the concept of a speaker.

A speaker makes a sound by moving the front of the speaker, which is called the 'diaphragm', back and forth rapidly. It's usually not very noticeable, but if you put a piece of paper on the speaker, it will 'dance around'.

Oscillation is the back and forth motion of an object. The oscillation of the diaphragm will also cause the air in front of the diaphragm to move back and forth.

But the air particles in front of the diaphragm don't actually travel away. It just oscillates back and forth. The oscillating air in front of the speaker will cause the air in front of it to also oscillate. It will then cause the air in front of it to also oscillate, and this process will repeat again and again until people perceive the sound.

The oscillating air beside people's ears moves, so it has kinetic energy. It can transfer the energy into eardrums, which people later perceive as a sound. So the speaker can transport the energy through the air without actually having to transport the air itself.

Kai took this concept for his improved shield. The oscillating air in front of his shield was moving, so it had energy. Kai then used that energy to soften the impact of the attack.

The concept might be a little weak, as it would be ridiculous to use it to block a strong attack like this. But Kai used a high frequency, high enough that humans couldn't hear it. After all, a human could only hear frequencies as low as about 20 hertz and as high as about 20,000 hertz.

He used a very high frequency, so the energy produced by it was bigger. And this magic circle made the air oscillate back and forth much higher than 20,000 per second. It created sound waves, but humans like Ayaka wouldn't be able to hear it.

It was only possible for Kai because he had his enhanced hearing. Kai used this high-frequency sound to send tremendous energy to soften the impact of the attack.

"Boom!"

Kai was pinned down to the ground by the fist. But surprisingly, his magic shield was still intact. This was the concept that let him block such a powerful attack.

Ayaka finally realized what just happened. From the aura alone, she could tell that this white ape was a high-ranking magical beast. This ape was possibly a B-rank magical beast, if not A-rank.

She immediately rose from the ground and charged at the ape with her spear.

"Get off of him."

The ape turned his head toward her and opened its mouth. Kai and Ayaka could see blue light appear in the ape's mouth. They immediately remembered what Shirotsuka Sanae said in class. High-ranking magical beasts like A-rank magical beasts or above might be able to use magic.

They immediately recognized that this ape was an A-rank magical beast. It wanted to shoot something out of his mouth toward Ayaka. But because Ayaka rushed toward this ape to save Kai, she couldn't avoid this attack.

She thought she was going to die by this attack as she didn't have enough time to dodge or to block this attack, but Kai suddenly grabbed the ape's fist and pulled the ape to his side a little.

"Boom!"

The ape shot out a ray of light from its mouth. But because Kai pulled the ape, its trajectory was changed. It missed Ayaka completely and landed on a nearby tree. It created a massive explosion, not losing to Ayaka's Explosion skill.

The ape turned to Kai once again and slapped him away with its giant hand.

"Boom!"

"Kai!" Ayaka unconsciously shouted his given name even though she had been calling him with his full name.

Kai crashed onto a nearby tree. His body was hurt all over, but he gritted his teeth and shouted. "I'm fine. Do you not remember our match? Cool your head!"

Ayaka shuddered when she heard that. That shout from him immediately woke her up from her anger. She was angry at herself. Because of her carelessness, Kai had to save her and was brutally punched by the powerful ape.

She tried to save him back, but it almost cost her life. Kai then saved her again, resulting in him being slapped away by the ape. But even after so many beatings, Kai shouted at her to wake her up.

The moment she woke up, she was filled with regret. Sadly, she couldn't do anything except beat this ape with her full power. She didn't act with her anger again as she had regained her cool.

She took a deep breath before charging toward the ape once again. The ape tried to charge its previous attack again in his mouth. When the ape shot it toward Ayaka, she dodged to the side and used her magic.

"Burn to Cinders, Flares."

"Boom!"

The fire hit the ape and exploded.

"Roar!" The ape screamed in pain. There was a batch of scorched fur visible on the ape.

The ape immediately entered close combat against Ayaka. But with its high strength and agility, the inexperienced Ayaka immediately got suppressed.

On the side, Kai finally crawled out of the tree he crashed into. He saw that the Ape was engaging Ayaka with close combat, and judging on their conditions, the ape had the upper hand.

Kai took a deep breath as his back was still in tremendous pain. He gritted his teeth as he started running toward the white ape.

When Ayaka saw him running toward them, she smiled. Kai was still fine. But in that moment of joy, the ape got a chance.

"Gah!"

Ayaka suddenly got punched on her stomach and spat some blood. She was blown away by that punch and rolled on the ground before finally crashing into a tree.

At the same time, Kai already reached the ape. He immediately swung his two swords at the ape while sliding between its two feet.

With that slash, Kai immediately separated the ape's two feet from the ape's body. He stood up again and grabbed the ape's hand. He suddenly threw the ape's giant body toward Ayaka because he could hear that Ayaka was still moving. He trusted her at this moment.

"Ayaka, Fire Net!"

Ayaka, who was bleeding all over, gritted her teeth while enduring the pain she was feeling at that moment. She raised her hand to use her skill. As soon as the red magic circle appeared on her hand, a large net-shaped fire appeared, catching the flying ape.

"Fire Net."

At this moment, she also trusted Kai. She used her Fire Net, forgetting why Kai was able to throw this giant ape away.

It was a single layer fire net that stretched out vertically. But as soon as the fire net caught the ape, the sound of scorching fire filled the entire field.

Ayaka poured all of her magic to roast this ape. Of course, Kai also didn't let her kill this ape alone. He immediately jumped forward and slashed both of the ape's hands, rendering the ape useless.

With the ape having lost all of its limbs, Kai used that moment to pierce his sword into its heart.

"Roar!" The ape let out its last scream before it finally died.

Ayaka then released her fire net and let the ape fall to the ground. Kai let out a breath of relief.

He walked toward Ayaka and helped her up. He stretched his hand to her.

"Are you okay?" He asked while looking at Ayaka's state. Ayaka took the full brunt of the ape, so her injuries were more severe than his.

But she was still acting strong. She tried her best to make a smile and said, "Of course. I'm fine."

She took Kai's hand, and Kai pulled her up. Ayaka couldn't regain her balance, so she almost fell, but Kai grabbed her and helped her stand.

She looked at the lifeless ape a few meters in front of her and turned to Kai. "We… really killed the ape, right? The A-rank white ape?"

"Yes," Kai smiled at her and nodded.

"Hihi… We did it."

"Yes, you're right," Kai nodded again.

Ayaka then tried to stand by herself. She wiped the blood on her mouth and asked. "How can that shield skill block that punch? If I'm not mistaken, it should also contain the same amount of power as the blow the ape had given me."

"It's my improved shield. Well, I took the concept of oscillation to make that skill. It's too long to explain, and it won't benefit you either."

"Hmph, I can look it up by myself later," She snorted.

Both of them smiled. Maybe it was because of this difficult battle, but their relationship somehow got better.

"You should rest first. I'll sea- Oh sh*t." Before Kai could finish his words, he suddenly noticed that a magical beast was coming toward them at a very high speed. He turned to Ayaka and shouted.

"Run!"

"Roar!" But before they managed to do it, the ape suddenly appeared in front of them and threw its right fist toward Kai.

"Oscillation Shield." Kai immediately used his improved shield to block the fist, but he suddenly felt something wrong.

Judging from the sound of the ape's muscle, it was contracting crazily on its left hand.

He immediately noticed that this fist was a fake, and the real attack was coming from its left hand. He saw its left hand move and immediately raised his Shield. Unfortunately, he could only make a single Oscillation Shield. This second shield was only a normal shield.

When the punch crashed onto his normal shield, the shield immediately shattered and the fist struck his abdomen.

"Gah!" He spat blood as the ape blew him away.

He crashed into another tree. Sadly, the ape didn't stop there. It immediately shot out that weird light toward Kai. As Kai didn't have a chance to react because of that strike, he was killed by that beam of light… or so she thought.