Yu Jin, or Jin to his friends, is the main protagonist of the webtoon and the candidate chosen by the King of the Chachaoongs, Jack to become his successor. Jin is a high school student who has been living in the human world when he is attacked by two random strangers. He is rescued by a man who wears a mask, calls himself Imae, and wishes to support Jin as the new king. Even so, Jin has no desire to become the next king and wishes to meet with Jack in order to get him to reverse his decision. Now, Jin finds himself in the middle of a conflict between those who side with him and those who want to destroy him and his companions.
Jin is a Korean high school student with red hair and yellow eyes. He is fairly short (170 cm) compared to most of the other characters, but that is due to him being young. On the back of his neck is an insignia which symbolizes that he has been chosen as the next king. It is only visible to other chachaoongs, who are able to sense it due to the energy it gives off.
Awakened: When Yu Jin is in his "awoken" form, he becomes a full-grown man. His hair grows out to nearly touch the ground. Although the top portion is still red, the tips fade to black; interestingly, this is the inverse of Bigak. He loses much of his wide-eyed, innocent expression and takes on a harder, edgier look through the face.
Jin is fairly serious; he does not think much about being alone, nor does he ever seem particularly bothered by the oddities of other people. In general, he likes a quiet life and just does not like to be disturbed. Because of this, he is not fond of the idea that so many people are now living in his house, although he tolerates it.
He will fight if provoked, likely due to the fact that he just does whatever is needed or necessary for any situation at hand. He is incredibly straightforward about his thoughts and opinions, and is frequently irritated by the people around him. Even so, he cares very much for others and will not hesitate to help if someone is in trouble.
In several cases, he is shown to be stingy about food and costs. He has noted many times about things being expensive, how Eunyul eats so much, and the fact that more and more people are being crammed into his house, requiring him to spend even more on them.
Awakened: Jin becomes much more assertive and confident, when awakened. His sense of justice drastically increases and he is far more ruthless when dealing with enemies. That said, he still stringently adheres to Jack's law and tries to avoid killing others, regardless of their actions. He behaves as if he is an entirely different person than his teenage self and is intentionally continuing to conceal himself. Although he recognizes the people he is dealing with, hints about past encounters with them, and speaks to them as if he knows them, none of them recognize him in his teenage form, even though they all feel he seems "familiar".
Although it is a fairly new ability, Jin has managed to materialize a few weapons, something that is characteristic of all chachaoongs. His awoken form seems to favor fusion similar to Imae.
Also similar to Imae, he is shown to be able to regrow his arm even after it is viciously ripped apart by another chachaoong, an ability most have never seen before.
He is also rather confident in his speed, when in his awoken form, explicitly stating this himself.
- Mirinae - She is Jin's human friend and classmate who often comes knocking on his door to go shopping.
- Imae - He is the one who reveals what chachaoongs are to Jin as well as protects him from attacks from other chachaoongs. Imae describes their relationship as master and subordinate.
- Shin Muyeong - He likes to think of himself as like a father to Jin. He has known the boy the longest, both having met one another as "humans". Mu-Young will do anything to protect Jin. If it were not for Jin, Mu-Young would still not care nor want anything to do with the chachaoong world.
- Eunyul - The owner of the Baekjeong Tal is tricked into nearly killing Jin before he is stopped by Imae. Since that time, Jin and Eunyul have developed somewhat of a brotherly relationship. They frequently pick on and torment each other, but seem to have become close friends despite the initial animosity between them.
- Ara - Yu Jin is largely indifferent to Ara's amorous advances, but she tends to inform everyone that they are engaged regardless of his wishes.
- When the mark first appeared on Jin's neck, all other chachaoongs felt it due to the energy, or aura, it emits.
- One of Jin's hobbies is making really bizarre combinations of food. He seems to be aware that they actually taste pretty terrible.
- He has decided that one of his goals in life is to make something Baekjong is not able to eat.
- He hates things related to the paranormal but is unable to identify why and feels almost as if the idea was "planted" in him at some point in the past.
- He is an impulse shopper, as demonstrated several times (though he seems to also feel buyer's remorse when he does so).
- Has deadly aim when throwing things—particularly when angry. Also states he will throw anything in hand, even if it is a knife.
As far as Yu Jin remembers, he was raised by someone he referred to as "Granny", but who passed away just prior to the start of the story. He still lives in her old house and attends high school like any normal Korean kid, although his workload is significantly greater than most students, as he has to both study and take care of himself. Beyond that, not much is known about his childhood besides that he met and developed a close relationship with Muyeong at some point in the past. He had nothing to do with chachaoong society and did not know of his true origins until he met Imae.
There have been many hints that Jin's past and his connections to the chachaoongs are far more complex than he knows, as evidenced by obvious deeper connections to chachaoongs like Imae, Bigak, and Eunyul. The greatest mystery in Part 1 is his true identity and reason for hiding.
Part 1 Season 1
Yu Jin is a normal high school student who dislikes paranormal topics and has normal, human friends. His life changes dramatically when he is attacked by two chachaoongs on the street, then rescued by a masked guy in a hanbok named Imae. After being told that he is the second generation king, Jin becomes determined to locate Jack and find some way to step down from his position. This refusal to take the throne causes widespread frustration in the chachaoong community, as Jack's power is dwindling (strong nonetheless) and the second generation cannot begin properly until Jin becomes king. Already frustrated that a "no-name" was declared king, instead of the one everyone expected, the fact that Jin is ignoring his responsibility has further frustrated those in the chachaoong community.
After the first attack, Imae moved in with Jin to function as his primary bodyguard. Muyeong, a long-time friend of Jin, returns from overseas travel and is astonished to learn that not only is Jin a chachaoong, but the second generation king, no less. He also decided to stick close to Jin in order to keep the boy safe, as he did not trust Imae. In order to hide his aura and make it easier for him to move around without being detected, Imae gives Jin a specially-created bandage to cover the insignia on his neck. Unfortunately, this has been only marginally successful in protecting Jin.
He is found and attacked shortly after by Baekjeong, who is vastly disappointed in the boy's fighting abilities. Baekjong would have killed him not for the fact that Jin briefly "awakens" and fights back. Baekjeong is startled when Jin suddenly refers to him by his name, Eunyul, since Imae was previously the only male chachaoong to do so. Muyeong and Imae break into the fight and Baekjeong realizes that he has been manipulated into attacking Jin. Baekjeong invites himself to stay at Jin's place—the second of the Tals to move in—though this was largely due to the presence of Imae than any real desire to be near the king.
Yu Jin is surprisingly tolerant of having Eunyul at his place beyond complaining about another mouth to feed, as Eunyul is a glutton, and noted to be a free-loader. Eunyul also makes it a point to bully the "newbie king" at every available opportunity.
Shortly after Eunyul's arrival, while Jin is out with a friend, he is spotted by Ara. She takes an immediate interest in him and stalks Jin back to his house where she immediately begins flirting and declaring her love for him. Jin is not particularly enthused with her advances, to the point of referring to them as sexual harassment. Nevertheless, he makes little effort to force Ara to leave when she takes up residence in his house (though it could have been because Ara is noted to be the strongest of the Tals when it comes to sheer physical strength).
Hanarin arrives the next day, having stalked Ara there. When Jin is not receptive to her staying there as well, Hanarin offered to read his fortune for him as payment, but realizes his past and future were both completely shrouded from her power, something Imae is glad to hear.
With four eccentric Tals at his house, Jin tries his best to balance a normal school life with the new-found weirdness at home and generally coping with being a reluctant king. But Jin continues to be targeted by others, and soon encounters a clumsy young chachaoong who stalks him to and from school several times with the intentions of attacking him. Fortunately, Jena's abysmal fighting skills pose no real threat, and with Imae's help, Jin is able to confront her to find out that Jagwi is behind everything, including the recent attack on Muyeong. After hearing the tragic story of Jena's family and how they are being forced to work for Jagwi, Jin offers to help set the three of them free. He extends this offer to Hiljo personally, promising that Imae will remove the marks on their bodies by which Jagwi controls them.
However, Jagwi confronts the group and murders Hiljo before Jin can free them. Jin is traumatized by watching someone die in front of him, and moves into a fully awakened state. This is the first time his appearance completely changes—he appears to grow taller, as his school uniform fits tighter on him, and his hair becomes extremely long, fading to black toward the ends. In this state, Jin has a much more imposing demeanor, and appears to know far more about his situation than his usual self. Though he refuses to kill Jagwi, he does injure him, removing the arm that was used to place marks on young chachaoongs. Before reverting back to his normal state, he also tells Imae to not get involved with Bigak.
It was after this incident that Jin begins having difficulty with his vision, worrying everyone. After human doctors can find nothing wrong with his eyes, the Tals decide to locate Saeha, one of few chachaoong doctors (and a Tal, at that). Saeha is summarily located and brought back to Jin's house. His assessment of Yu Jin's eyes is that it has to do with Jin using his abilities to change his appearance. Jin denies that this was the case, and claims to have no knowledge of how to do this in the first place. Though Saeha is doubtful, he assures Jin that his vision should return to normal soon and prepares to leave. But upon realizing that Ara is living with Jin, Saeha states that the latter's condition is very serious and he will have to stay to keep an eye on his situation, thus becoming the fifth Tal to live with Jin.
Jin plays a largely tertiary role in Muyeong's arc though he is nearly devastated when it seems that Muyeong would die from Leon's venom. Even his awakened self is determined not to let Muyeong die. When Cheoyong finally forces a confrontation between the twins, an awakened Jin appears with Imae to stop him from killing Ignatio. Cheoyong makes it very clear that he does not like Jin and loathes him for refusing to take the throne. He would have fought him then and there, if not for the fact that Jack wordlessly intervened. After shooting Jin an unfriendly glare, Cheoyong retreats with Jack, and lets Ignatio live and Jin return to his normal life.