"Yo, my beloved student. You have finally come."

Seeing the familiar face that had instilled a trauma into him, Kai's face distorted a little bit. With a normal expression, Ria Ross pushed the door wider and waited until Kai regained his calm before saying, "Come on, you brat. I didn't teach you to have that kind of expression."

Kai took a deep breath before he said with difficulty. "Nice to meet you again, Teacher. It's been a few years."

"A few years? It's been ten years, six months, fifteen days, and twenty-three minutes." Ria Ross snorted. "By the way, the timing is when I last saw you at the Airport a decade ago."

"You even know the exact time…" Kai sweated profusely, trying hard to control his calm expression.

"Haha…" She laughed out loud before taking a look at Michelle and the others. "Hmm… You even bring the Shadow Princess, Space Girl, and Little Aries."

"Space Girl?" Tasha opened her mouth in surprise, not knowing where the nickname came from.

"Little Aries…" Ayaka twitched a little bit as she had been calling her with that name after finishing the operation.

Meanwhile, Michelle didn't have a change of expression because many people in school called her that.

"Anyway, come in first." After pushing the door wide open, Ria Ross walked inside while waving her hand to ask them to come.

Kai took the first step inside, following Ria Ross to her study room, where Ayaka asked her to make her a zodiac.

"Welcome to my house and also, happy birthday, Kai." Ria sat down on her chair as she greeted them once again. "As you have seen, this is my study room."

"Uhm." Kai thought for a moment and said, "Why do you call me here?"

"Haha… Why do you ask that question? Do you want to go back now?" Ria placed her hand on the table before supporting her chin.

"No…" Kai glanced left and right, not knowing what to answer. He took a deep breath and looked at her with a serious expression. "I mean, Teacher isn't someone who suddenly asks me like that. I think Teacher has something important and wants me to see it."

Michelle and the others didn't let out a single sound and watched how their conversation unfolded. Only Michelle knew that Kai actually overcame his trauma a few years ago because he knew everything she did would consider him first. If not, she already continued the Zodiac project instead of giving it to the government. However, Kai didn't act with confidence because no matter what he did, Ria always outsmarted him. No one would be happy when they always lost unless they were a masochist.

"You are right. I have a few things to tell… just like the reason you come here." Ria Ross proved Michelle's thought once again. "Let see, you are coming here… first is for that girl, little Aries. The second reason would be the upcoming Raid Mission in Canada. The third is to fight me again."

"Everything except the third reason is right." Kai closed his eyes and shook his head helplessly.

"Hahaha… I let my intention slip." Ria Ross fixed her grey hair while grinning.

"You are purposely letting it slip."

"Haiz. This is my fault to teach you not to leave small details… you are picking it on me right now." Ria sighed in defeat.

"Teacher, We have enough of your jokes." Kai scratched his cheek, putting a weird smile.

"Fine." Ria shrugged before turning around and reaching a long briefcase behind her seat. She laid the case on top of her table before opening it.

"!!!" Four of them were amazed as soon as they found out the thing inside the case. It was a pair of swords they saw a few months ago.

The black handle with a few white straps to soften the contact with the hands. The sword had two colors: Black as the base color and a green pattern like Kai's magic circle. One spot stood out the most. Right above the handle was a spherical metal. It looked like a glass made of metal while the inside was empty.

Ria looked at the swords first before explaining, "I have remodeled according to your problem. Thanks to the concept of little Aries, I only need to search for a metal that wouldn't break because of the vibration."

"Ah. It's Teacher's specialty." Kai nodded with a smile.

"Specialty?" Ayaka was the most curious one about this. She had stayed inside this house but knew nothing about it.

"Teacher, what kind of training do you actually give?" Kai furrowed his eyebrows, not expecting Ayaka not to know Ria's magic.

"Hmm… I only taught her Martial Arts to refine her fighting style. She… I don't use my magic at all." She shrugged.

Ayaka looked down, ashamed, and commented, "Professor Ria. You don't need to mind talking about me. You can just say I am too weak for you to use your magic. You don't even use your hand."

Kai stared at Ayaka for a few seconds, knowing how she felt. In fact, he could only make her use her hand after four months of continuous fighting. Kai explained, "She is A rank Earth Magician. However, she somehow managed to evolve her magic like Michelle's Dark Magic into Shadow Magic. So, her magic now is Metal Magic. In fact, Michelle got the inspiration of Shadow Magic from her."

"Yeah. It was after you became a Zodiac. I thought about getting stronger and somehow stumbled at her place." Michelle nodded. Ayaka was astonished to hear this, while Ria Ross looked annoyed.

"Enough about that talk! Take a look at the body of the sword first… I have combined a few metals and made it durable to work under high vibration. It's not really hard to make this because there is already a record of this from the previous era. The problem would be this spherical thing that will hold your vibration." She pointed at the spherical spot.

Kai and the others observed the spot. "How much vibration can this take on?"

"I used the Supersonic Blade video as my reference. The wave can vibrate the blade twenty thousand to forty thousand times per second. It's only used in bakeries though. This one can handle one hundred thousand to one hundred fifty thousand vibrations per second. The sphere was very brittle previously and kept breaking. It only stopped breaking after I changed the metal into the hardest one that I could synthesize."

Kai nodded before taking out the sword from the case. "Can I test it, Teacher?"

"Sure. Just get a bit farther away, since this is a double-edged weapon." Ria Ross nodded before pointing at an empty space in the corner. "You can try to swing it around in that place."

Kai glanced at the empty spot, nodded, and walked there. He made a few swings and said his experience. "The weight is the same as my previous sword, and the length is also similar. The sphere is disturbing me a little, but there should be no problem in the performance. I just need some little adjustment."

"Sure. There should be no problem with the design. How about you activate the vibration?"

Kai nodded and created a magic circle that enveloped the sphere. This spherical magic circle was to reflect the sound completely, so it would keep crashing to the metal and let the sword vibrate.

Kai waited for a while to let the sword vibrate. Although he couldn't pinpoint it, it looked like the sword was vibrating one hundred thousand times per second. There wasn't a change in the sword's appearance because it vibrated at speed high enough to be not visible with naked eyes.

"Cut this one." Ria threw a wooden log at him.

Without hesitating, Kai slashed the wooden log. Surprisingly, it had no resistance from the sword as it was sliced into two by his sword.

Ria didn't stop there. She quickly grabbed a piece of metal and threw it. "This one next."

Kai sliced the metal once again.

*Clang!*

Surprisingly, a metal clicking sound echoed across the entire room even though the metal was sliced into two.

"How is it, Kai?"

"There is a resistance from the metal for a split second and takes away a portion of the vibration."

"Hmm… As expected. This is why we separate fantasy and science." Ria let out a long sigh.

"Yeah. It can coexist, but it wouldn't be the same as our expectation." Kai nodded.

Michelle and the others were confused by their conversation but kept their silence until Ria explained it. "There are a few problems in this Vibration Magic. The first problem will be science itself. People tend to think it will be an overpowered weapon. Yet, in reality, we need the material that can stand the vibration. And another one is the resistance he felt earlier, he will need to keep pumping the sound to create more vibration. In other words, the fantasy story has been broken by this science.

"The second problem is about the design. It's hard enough to make a design that can stand a high amount of vibrations. You can't even see the sword vibrating because it's vibrating very quickly. And there is this shock breaker, so the vibration doesn't flow to the handle and the user. It took me three years just to design this.

"After that, the sharpness. It indeed increases the sharpness but not at the level it can cut through anything. The metal I threw at Kai was a brittle metal, and it already gave a resistance. If it were a hard magical beast's shell or a harder metal, he might not be able to cut it. Of course, he can just increase the amount of vibration, but it comes back to the first problem. The conclusion is this Vibration is good but not overpowered… Such a shame." Ria Ross shook her head in disappointment.