Past.

~ Earth, South-Korea, Seoul. Summer 2019.

Two girls, Yama HARU and Park BOYEON were working at a cheap cafe in Seoul. Their dream was to become famous singers, but luck wasn't on their side, until, one day, a famous idol, SHIHO, entered their cafe. He was impressed by them, thus decided to invite them to a party with popular celebrities, that was supposed to open the doors to success.
Although that party didn't get them cast by any entertainment agency, the girls had a way to approach the idols, member of a famous k-pop band: the FloHwa.
BoYeon found out that her ex boyfriend, with the stage name of RONIN, was the leader of that band, despite his troubled past.

In a desperate attempt to prove to BoYeon that he changed, and to convince her to give him another chance, Ronin invited her, Haru and their friend TOKI to a camping in the mountain near Seoul, for a weekend.
The other two members of FloHwa, CRIO and APPLE, plus ShiHo joined them for the camping weekend.
BoYeon, who had been shot by accident by Toki some days before, tried to hide the truth from the others and spent most of her time sleeping in her tent.

In the evening of their arrival, the young Apple went to take a walk near their camp and by the shores of the lake, he witnessed the weirdest possible scenario: three men, dressed in historical outfits, were bickering inside the water. It was very cold and it made no sense that someone would go to take a bath, especially in those clothes.
The three, paradoxally, looked very alike some idols of their time, which convinced Apple and the others to believe that they were indeed the singers and actors they knew, going through some psychological condition.
The members of FloHwa phoned their idol friends and surprisingly, they all answered and proved to be far from them. The three men in historical clothes were indeed just lookalikes.
Haru was very shocked to find out that JeongJong looked exactly like her husband PaOh, while Chungseon like her old friend Taeseokjong from her original world.

The three were time-travelers, Kings belonging to different ages of Korean history: Jinheung from Silla, JeongJong from Goryeo and Chungseon of - later - Goryeo. While the three couldn't agree on anything and kept fighting each others, the guys from the present decided to split them and take them home with them, so that they wouldn't be given the chance to stain the reputation of their idol friends.
JeongJong returned with Haru and BoYeon, Chungseon with Toki and Jinheung with ShiHo.

For the three ex Kings, adapting to this new age was simpler than expected, after the initial troubles. A couple of months after their arrival to the present times, JeongJong, better known as Wang Yo, founded his own entertainment agency (RYEO Ent) while Chungseon, Wang Won, founded his own building company (YUAN Constructions).
Crio, worried about the plots these time-travelers could play against the present people, kept opposing them in every way he could, unsuccessfully.
He was eventually forced to stop bothering about Yo and Won, when his younger brother YOONMIN attempted suicide, for unknown reasons.

While KIM YOUNGHYUN, father of Crio and YoonMin was driving back to Seoul at full speed, to reach his youngest child at the hospital, he almost hit some mysterious person wandering the street. It was night and he managed to stop his car just in time not to kill him.
As he tried to assist the young man, he realized that he was dressed in a ruined and ancient-looking robe. Although he was certain to have stopped in time, the boy was covered in blood and seemingly close to die.
The man carried the passed out stranger to his car and drove him to the hospital where his son too was admitted (in questo caso, questa parola significa 'ricoverato). YoungHyun paid for the care of the mysterious boy too, who was found to have never been vaccinated.
The man also took the beautiful katana the boy had with him, locking it in the trunk of his car.

As YoungHyun called the police, the older brother of Apple, DookGuk came to receive his report and took the sword to the police department as a proof for the investigations connected to that boy.
The next day, Apple went to visit YoonMin at the hospital and he accidentally found out about the new person. Hearing what YoungHyun said about him, Apple got to suspect that the stranger could be another time-traveler, as he too was found near a lake in historical outfit. The young singer promply warned the others through their WhatsApp group, summoning Haru, Yo and Won to the hospital.

The four had their first contact with the awakened boy, who proved to be indeed another time-traveler, but from the early Joseon era. He introduced himself as GongPo, but asked to be called Tero (the japanese version of his name).
Tero claimed to be a Crown Prince, son of King Taejo of Joseon, although there seemed to be no track on him in the historical records. As a matter of fact, his parents made sure to eliminate his name from history, after their attempt to get rid of him in favour of his younger brother.
At first, the relationship among Yo, Won and Tero was extremely tensed. The new time-traveler was terribly hostile towards the others.

Tero escaped the hospital and ended up befriending YoonMin. Following his violent and rather evil nature, Tero soon accessed the criminal environment and made himself a name among the worst criminals of Seoul. He formed his own gang together with the crazy driver Aron, the ex indonesian soldier Awut and the haker JaeJoon. Tero created himself a fake identity, also with the help of Sato, an old Japanese man who was hired to pretend to be his father.

After reaching a very advantageous position, Tero attempted to approach Yo and Won again, offering them help to increase the earnings of their societies. The three begun a weird and not too stable friendship, that led them to get closer to each others, nonetheless. Tero hired Won's company to build him a special house in the mountains and sent a young, promising boy to Yo's agency: Shin KITAE.
The young orphan turned out to be less successful than they expected, but both Yo and Won ended up developing a fatherly affection towards him.

One night, a weird man came to knock on the door of the dormitory where Haru, BoYeon, Yo and Won were living. The man, after having a secret conversation with the girl, convinced the two ex Kings to be a time-traveler like them and, in the specific, the first son of Yo, Gyeongchunwon. (The actual historical name of the son of JeongJong.)
Gyeongchunwon started to work for the police department, as a coverage.
In truth, he was no less than the Commandant of the Emperor of Xhuanghen, Hu HYUNKI, son of PaOh, husband of Haru. The real reason of his arrival was to investigate on the disappearance of his father and he was very suspicious that Haru could be behind it.

Weeks after his arrival, HyunKi accidentally discovered a particular fact about KiTae: a birthmark at the bottom of his belly, a half moon, identical to the birthmark every other Yama, children of HIRO, had on their body. This fact proved that KiTae was actually the younger brother of Haru and caused HyunKi to turn even more suspicious.
Being the Yama family all wanted as criminals, for the abduction of the princes ChangMi and XinLi, sons of Emperor LianBi, the Commandant captured KiTae and escorted him to the Palace for interrogations.
There, they found out that KiTae was a half-human and half-auriold.

Worried by the happening, Hiro, the father of Haru, forced his daughter to return to Shiixia, the secret island where all shinobi lived in safety.

Yo, Won and Tero noticed the sudden disappearence of Haru, HyunKi and KiTae and were worried for their safety. They struggled to search them with all of their means, also with the help of police and criminals, but their efforts led them nowhere, until, one day, a mysterious man appeared on their door. He was identical to Yo, in looks, although ragged and skinny. It was PaOh, whom introduced himself as ZHENDONG YICHUAN. Why? Because he was a great troll and loved to annoy the General, his archenemy.
PaOh explained them all that the person they thought to be Gyeongchunwon was actually that bastard of his son, HyunKi, and that it had probably been him to take Haru and KiTae away, to their original world, Nortrig.

Convinced by PaOh, Won, Yo and Tero, with his whole gang, prepared to head to the capital of Xhuanghen in Nortrig, Shiirhuang, to 'assault' the Imperial Palace and rescue their people.
While for PaOh it was all a big joke, the same wasn't for Tero whom ended up crossing the path of JUNYIN, a powerful fighter with a very weird nature. Tero could stand no chance against him, but still managed to wound JinYin. His blood, though, wasn't normal, it was like a poisonous lava that started to burn his armor and body like acid.