The back of the moon, mysterious, dark, unknown to the Earthlings. It never faces the Earth, so the city beneath it was hidden from the Earthlings.

From the surface of the back of the moon, some stations camouflaged as rocks were standing on the uneven surface of the moon. Some whirring sounds came from them, shadows coming in and out of it.

The Artemis call these stations as The Lift. It sends people up and down to their destinations, some invincible space aircrafts taking off near the stations.

Tzuyu was standing inside The Lift, exhausted from her trainings on the grounds. Being the heiress of one of the two strongest Guardian family - the Chou's, she was trained hard to be the strongest amongst her family.

Her hand band rang with a beep sound. Checking her wrist, Tzuyu saw the call was from her dad and she answered the video call.

"Hi dad," she greeted, a small smile curving her lips upwards in a beautiful way. The Lift was going downwards into the deep, so she would have some time to answer the call.

"How's my girl doing?" Mr Chou smiled, he could see the sweat on his daughter's forehead, knowing that she'd trained hard for the future.

"Fine, just a little tired from my trainings. What brings you calling me so early today?" Usually Tzuyu's dad would call around evening, but it's only noon so she was confused.

Mr Chou chuckled, "Can't I miss my daughter?"

Tzuyu smiled, "Come on, you just seen me this morning before you left our house to office."

Normally the Guardians don't smile a lot, in fact, when they smile you're going to think that you're doomed. But for family members, they do smile towards each other - it's not that they don't smile because they're heartless, it's just a form of protection.

"Come to the Great Hall, me and Uncle Yoo have something to tell you. Oh, and you might meet the heiress of the Yoo's family, so just freshen yourself a bit," said Mr Chou, finally revealing the reason of why he'd called.

"I'm fine with meeting Jeongyeon unnie, it's not that she never meet me after my trainings, she's used to my messy look," said Tzuyu playfully.

Mr Chou sighed, "Tzuyu, you do know when we're in the Great Hall we're supposed to be in formal suits, right?"

"I do, I won't forget such important things. I'll see you later, dad," with that, Tzuyu cut off her call with her dad, as her lift had already reached its destination - her home.

This was the second time Tzuyu entered the Great Hall, but she couldn't stop herself from looking at all the carvings on the wall, the murals and short poems etched in the wall, telling stories from thousands of years ago.

She'd dressed in suits, her long hair tied back in a ponytail.

Her footsteps echoed in the long hallway, and as she reached a huge silvery door, the two guards standing aside pulled the heavy door open.

There, she saw her father, Mr Yoo, Jeongyeon and of course - the one who will always be in the Great Hall - Queen Artemis.

The Great Hall was normally used for assigning important missions, where the Guardians are appointed to some of the countries on the Earth. The Guardians' role was to keep the Earth in check that there was no intruder from other places than the solar system itself.

This helped to keep peace on the Earth for many years, and has never failed to do so.

Tzuyu bowed with her right arm folded in front of her chest and said, "Good afternoon to you, Queen Artemis, Father, Uncle Yoo and Jeongyeon-ssi."

Queen Artemis is just a cover up name for every Queen or King in the present era, in which they don't use their real names to be called at. Nobody actually know how the Queen or King chose their next heir, but it was always clear that they are incredibly powerful, strong and intelligent. Although Artemis is a Greek goddess, but this name is given as an honorific to the current King or Queen.

Therefore, Queen Artemis always wear a thin silver mask, hiding their real identity, which is to prevent criticism if the present King or Queen is from a lower class family. That is to say, the King or Queen does not necessarily come from a upper class family, nor from the Guardians family, and may just be a normal citizen who lives in the Moon.

As Queen Artemis had held her hand up, Tzuyu straightened herself up.

Queen Artemis nodded, "Good afternoon. I assume you and Jeongyeon had knew why you two are here, alongside with your father?"

This time Jeongyeon spoke, "Yes, my Queen. Tzuyu and I were assigned missions."

"Yes, my girls. But not only that, this mission is closely related to your final training as the heiress of the Chou's and the Yoo's, as this is classified as Level S mission. To say that, this mission is highly dangerous. You may meet some of the most dangerous outer solar system life forms, so you two should prepare yourselves," answered Queen Artemis.

Both Tzuyu and Jeongyeon nodded with a stern expression.

"Your equipment will be shortly delivered to your house, and then the two of you will depart from the Moon to the Earth tomorrow morning."

"With that, you two shall be dismissed. I still have some discussions with your father, so you may leave now," Queen Artemis stated.

Jeongyeon and Tzuyu bowed again, then straightened up and left.

As they walked down the long corridor, two of their family trainees - in fact, the best trainees of the Chou and Yoo family - Hwang Yeji from the Yoo's, and Shin Ryujin from the Chou's - were walking towards the Great Hall.

"Jeongyeon sunbaenim, Tzuyu sunbaenim, good evening."

The both of them had greeted the two elder ones, nodding towards them.

"Good evening, Yeji, Ryujin. Getting missions?" Jeongyeon asked.

The two younger Guardian trainee nodded eagerly, "This mission is going to help us to pass the Guardian's test, then we'll be the Guardians after it," said Ryujin.

"We'll get going," Yeji said, and both pairs parted ways with the trainees going towards the Great Hall.

"Wanna have a dinner at the cafeteria?" Jeongyeon asked, pushing her glasses that slid down her nose bridge.

Tzuyu nodded, "Sure, let's go."

In the zero gravity combat training room, two shadows were fighting each other with strikes that are hard and sharp. There were two figures standing beside the combat circle - one shorter, the other one taller - watching the two s