One week later, Kai smiled at his parents in front of the train that would soon leave the station. "I will be going for three months. Take care, alright?"

"Yeah. Unfortunately, Tasha can't see you off."

"She is busy with her matters, especially since she is preparing for her graduation. She will be gone for a month or two too."

"We know it." James Carter nodded and patted Kai's shoulders. "We can only watch the news from home and can't help you with a single thing in your job. Although you might have grown tired of hearing this, I will say this no matter how many times I need to say it. You will always be our pride and joy, so please take care of yourself."

"Of course. You two should also take care of yourself since Tasha and I won't be home for a few months."

"Don't worry. We both will be fine." James nodded while smiling at his wife that agreed with him. "Go pursue what you want. If you feel tired of everything, just come back home and talk to us. We will lit the fire in your heart once again."

Kai smiled and hugged his father and mother before coming inside the train. "I am going."

"Yeah."

The train soon moved, heading straight to the station near Ria Ross's house.

The journey didn't take too long, and Kai immediately went toward the rundown house that had a very different look between inside and outside.

He knocked on the door of the rundown house.

As if she had been waiting for him not far from the door, she opened the door one second after he rang the bell.

"I have been waiting for you." She smiled.

Kai looked at her messy clothes and the bag under her eyes. "Did you sleep last night?"

"I did! I am a responsible adult."

"How long?"

"One hour."

"That can only barely be called a nap. What adult?" Kai sighed and opened the door wider, so he could go inside. "Have you cleaned your room yet? You didn't clean your room the last time I came here with the others. And Ayaka told me you didn't clean it when she came alone."

"Ahaha…" Ria Ross scratched the back of her head and looked away.

"Anyway, I will be living here for three months, so I will clean this place up first. For now, how about you sleep for a few hours."

"I will eat first and take a shower." She let out a long sigh as if Kai would keep nagging her unless she did everything necessary.

"…" Kai sighed. "I still remember how you never cleaned up your room even when you trained me a decade ago. Geez. You need to enjoy your time, you know."

"Shouldn't you be grateful that your teacher is a workaholic? You can get everything in time, and it's not like I have any problem in daily life." She shrugged.

"You are going to collapse soon, you know. Maybe I shouldn't ask anything from you like I did in the past ten years. Right, I heard from Sir Nathan that you led a better life when I didn't…"

"Fine, fine. You just want me to rest, right?" She sighed. "You were always like this. Even though I had bullied you the whole day, you kept nagging me to rest with you because you didn't want me to fall sick."

"So, you do realize that back then, you gave me a trauma?" Kai twitched his eyebrows in annoyance.

"That wasn't trauma. You just got used to pain. That's the most basic thing you need to have on the battlefield other than fear resistance like opening your eyes when your enemies attack you or techniques," She proudly claimed.

"Whatever. Anyway, what did you eat daily?"

"I just ordered it online or some instant noodles."

"I bet you ate them when they had become cold because you were too focused on your research."

"They tasted the same." She shrugged as if it wasn't a big deal.

"Anyway, you will have a healthy lifestyle when I am living here. If you don't abide by this, I won't follow any of your instructions."

"Fine. Even if you want me to burn all my research, I will do it." She gave a thumb up, telling him that he was more important than everything she had.

"Yeah, yeah. Go get a healthy lunch first and take a shower. I will handle everything." Kai sighed.

"Alright. Before that, do you want to eat too?"

"Nope. I have eaten not long ago." Kai waved his hand.

She and Kai then went to the room where she found her device and ordered food there.

Kai facepalmed when he saw the room. Papers were on the ground, and everything looked messy, including the trash.

"I will take a shower right now." She immediately escaped.

Kai looked at her back and shook his head with a helpless smile. She looked more energetic when he came, so he just ignored everything and proceeded in dealing with this mess.

A few minutes later, she returned to the room, finding Kai had thrown all the trash and fixed a portion of the mess.

He glanced at her and said, "I have heated the food."

She looked at her table, finding the food she ordered earlier while piping smoke. Walking to the table, she sat down and started eating.

"By the way, how are you doing, Teacher?" Kai asked.

"I am good. I have found a solution for the side effect of your Lion Blood that makes you go berserk. However, I still need various tests to see if it's safe for you or not and wait for the highest quality materials. And I found out that the solution can increase your strength even further as if it unleashes the suppressed ability in that blood."

"That's good to hear, but won't that be snatched by the government again?"

"I have never submitted or discussed this with other people, so I am good. It's not like anyone can hack me." She shrugged. "The reason I didn't do anything with my baby, the zodiac project, was because I had enough with it. Well, you could say I was content with just you."

Kai smiled and nodded. "Thanks."

"Hehe. Oh right, I have meant to ask you this question, but what is your purpose for coming here? I know that you want to train, but I don't know the specific."

"I will be figuring out the new magic that I have been working for."

"Ho? I am a little curious about it."

"Well, you will know eventually, so I guess there is no need to hide this." Kai hesitated for a second. "The concept comes from the Sonic Boom."

"Ah, so that's why you want me to create a weapon far stronger than the one you have right now." She nodded in understanding. "Although I don't really know the details of your plan, I can somehow understand that the Sword needs to withstand the pressure."

"Yeah."

She recalled everything she knew about the sonic boom and muttered. "Sonic Boom…The phenomenon of a shock wave was created when an object travels through the air faster than the speed of sound. The shock wave itself is enough to cause small damage to the surrounding. And I believe it can complement your Vibration Sword and bring out something far more terrifying than a normal Sonic Boom. If it can cause substantial damage, I believe it is deadlier than your Vibration Sword alone."

"That's the concept, but I don't know if I will succeed."

"But you know that a sonic boom does not occur only at the moment an object crosses the speed of sound; and neither is it heard in all directions emanating from the supersonic object, right?"

"Yeah. The boom is a continuous effect that occurs while the object is traveling at supersonic speeds, but it affects only observers that are positioned at a point that intersects a region in the shape of a cone behind the object." Kai confirmed.

"Then, how are you planning to use it? The continuous effect alone is hard to achieve."

Kai smiled and took out his weapon, slowly swinging downward. "You see this sword? It's a normal swing, right? But Teacher should already know that it cuts the air."

"Indeed." She nodded, fell silent for a moment and opened her mouth in surprise. "Interesting."

"Yeah. That's why I want to try it. When I swing my sword downward, it cuts the air. However, we can explain this in another way. Because the sword travels here, the air is forced to move, resulting in a wind flow from the bottom of my sword to the top of my swords. Just like how airplanes fly because of the difference of velocity between the air flowing on the bottom and the top spot of the wing, this one uses the same technique.

"Of course, instead of the difference of two, I will classify it as three parts. The bottom of the sword, the sides (left and right), and the top. This way, I can generate enough wind pressure to make the sound flow.

"After that, through my Vibration Sword magic, I will amplify it even further, so the swords vibrate faster than the speed of sound. It will increase the Sound Wave in the sides before flowing to the top of the sword. Of course, the front has quite powerful energy too, when I use this concept, but it's nothing compared to the sides and the top of the sword.

"That's why I asked Teacher for a stronger sword. It's to have a more powerful sword body to withstand the speed of sound. As for the thunderclap sound every time Sound Boom occurs, I will try to fix it by controlling the frequency. As long as it's above human ears can perceive, it will be alright." Kai smirked.

"Interesting. This time, you might be able to kill me if you succeed in this technique. I am looking forward to it."

"Yeah. That's why you need to sleep first. I want to fight you in your top condition. Of course, a month from now." Kai smiled.

"You bet."