This article contains details from the manga that are not covered in the anime. Proceed with caution.
Zeno (ゼノ Zeno?) is the Original Ouryuu (Yellow Dragon in english), one of the four Dragon Warriors and he possesses the blood of the yellow dragon deity. Later, it is revealed that he is actually the original Ouryuu who once served King Hiryuu 2,000 years ago. Later on he became the fifth person and final dragon to join Yona and Hak on their journey.
In the anime (manga chapter 1-109) Zeno is shown/known as a young man who always has a smile on his face, which indicates that he is a cheerful person. He has blue eyes (previously brown) and thick, messy yellow hair. Over 2000 years ago, King Hiryuu gave Zeno a necklace of alternating, round burgundy and blue oblong beads with the centerpiece being a golden disc with a dragon on it. Originally, Zeno wore it as an ordinary necklace but currently wears it around his head, under his bandana, with the disc hanging out on the left side of his head, in front of his ear. He is considered very handsome.
He wears an orange overcoat with diamond patterns on top of a white robe with brown hemlines, fastens a green scarf around his neck, and dons brown short boots.
When Zeno's powers are activated, the part of his body that regenerates becomes covered in yellow scales that are as hard as steel, also temporarily giving him powers similar to Kija if his arm regenerates and Jae-Ha if his legs regenerate.
Zeno is an energetic, cheerful young man who enjoys the company of others. He mostly uses third-person speech (the habit he probably picked up from Kaya) and rarely calls anybody by their given names even after learning them (he calls the dragons by their titles, ex: Seiryuu or Ryokuryuu) Most of the time, he appears to be childish and rather attention-seeking, though he has his wise and mature moments, being 2000+ years old. Despite the fact that he chooses not to fight, he always stands on the front lines to protect everyone from danger.
Like Jae-Ha, he can easily discern what is happening to a person and even has foresight on them, like when he tells Hak that he has "the smell of death" on him or how he says that Tae-Jun has changed and that he can become someone important. He also appears to know more than what he is willing to tell and may appear deceitful because of it. However, he actually waits for the right time to tell things as he can’t easily show or express it to others given his circumstances of being one of the original dragon warriors.
Zeno can be very lovable, and at times he tends to try to break up Kija and Hak's arguments. He especially loves food, which is what first got him in to the group in the middle of a forest, before the other dragons revealed his identity. According to Hak, Zeno "broke Kija's record of speed joining".
Two thousand years ago, Zeno was just an ordinary kid who could hear the voice of God like Ik-Soo. When Ouryuu descended from the heavens to look for a human who can be his other half, Zeno decided to take in the dragon’s blood in a wish to make the world a better place and for everyone to be happy. Since then, he has stopped aging and no longer hears the voice of God.
He joined Gu-En, Abi and Shu-Ten, who were the Hakuryuu, Seiryuu and Ryokuryuu, respectively. During the conflict in Kouka, the four of them protected King Hiryuu. One time, the other dragon warriors became curious of Zeno's powers and he showed them how he is able to regenerate fast. When he showed it to King Hiryuu, he was hugged by him and was given a dragon crest. Several days after, he became worried about the nature of his power and he asked the king about it. However, the answer to his question remained a mystery as King Hiryuu died.
After the death of the king, he appointed himself as the "Priest"--with the dragon crest proving his authority--and chose to stay behind when his dragon brothers left. Before the three departed, they shared a hug as Gu-En told them how they were all connected and how they will return to the heaven someday. However, Zeno at the time had come to learn about his power and thought that he could no longer return anywhere. During the time he was a priest, he solved the dangers coming to the country on his own. Twenty years later, he sensed the fleeting life of Gu-En and he became depressed as he pleaded with King Hiryuu and his dragon brothers to not leave him behind.
Unlike the three original dragons, he did not establish a village of his own. He had left the village he was born in and commented that there is not even a shadow of what was originally there. Since he was stuck in his immortal body and did not have a village he belonged to, he traveled around a lot. At some point in his life, Zeno was married to Kaya, a girl living on the outskirts of a certain village, she died at an early age due to an incurable disease. A while after Kaya died, Zeno traveled again, but after realizing that King Hiryuu may reincarnate and seeing the red dawn (the sign in the sky of the newly born reincarnation), Zeno decides that since he has waited for so long already, he might as well wait just a little longer. When Yona was born, knowing she was the reincarnation he had been waiting for, he watched over her until they day they officially met.
-During Zeno's travels, he often got frustrated/depressed and remembers a time when he tore his body to shreds. Whenever this happened the dragon's crest always calmed him down.
Immortality: As the possessor of Ouryuu’s power, Zeno has an infinite lifespan. Due to this, he has stopped aging, giving him the same appearance as when he drank the dragon’s blood two thousand years ago, and can’t get sick even if he is away from the Hiryuu Castle, unlike the other three dragon warriors.
- Regeneration: Zeno can regenerate quickly from the injuries he receives, which cause the dragon scales to form on his body after he heals. Depending on where the dragon scales form, these parts of the body cannot be hurt any further once they regenerate. This explains why Zeno did not appear to have an indestructible body and could be easily hurt like a normal human in the beginning, as it was necessary for him to be hurt deeply on certain areas of his body. Furthermore, even if a part of him is cut off, Zeno can still control it at will and reconnect it back to his body. However, after a while, the injured parts of him that turn into dragon scales return to its normal human form. Even though he doesn't get sick from being far away to the Hiryuu Castle, his regeneration slows down.
Melee Combatant: Despite looking like a person who doesn't train his body, Zeno can handle fights against numerous soldiers, armed or unarmed. This is further enhanced if Zeno gains the dragon's scales on his arms and feet which gives him immense strength similar to Kija's dragon claw and Jae-Ha's dragon foot. He mentioned in a later chapter that he once gouged out his eyeballs, but all that did was make his eyes "super strong". Nevertheless, he mentions that he has always had good vision.
Other: Just like the other dragon warriors, Zeno's soul seems to be able to protect Yona in desperate situations, when he and the others can't.
- (To Yona) "Well miss, that's splendid. But everything that lives, will return to heaven one day." 
- (To Hak) "Even if we dragons die once, we will be replaced someday. But no one can replace you, big brother, so you must treasure yourself." 
- (To Hak) "I might be the odd picking of the dragons, but I'll make sure that I'll protect all of you with all my might." 
- (To Yona) "I am the dragon that was born to be your shield. If Ouryuu, your shield, protects you...You will never...be injured." 
- (To enemy soldiers) "No matter how many times you tear me apart...I will be everyone's shield." 
- (To an enemy soldier) "What will you do? Unlike you, I have no limits. I can go on fighting for hundreds of years. Come at me, I have all the time in the world." 
- (To The Dark Dragon and the Happy Hungry Bunch) "Are there more questions? Are we satisfied? Then we're done, we're done!" 
- (To no one) "From the weight of the passing years, with all the severe pent-up frustrations, there were times when I tore my body into shreds. During those times, this Dragon's Crest, calmed this heart which was falling apart." 
- (To Kija, Shin-Ah, and Jae-Ha) "You guys get way too worried about me fighting! I literally can't die, so its 100 times safer for me than you! No more mother-henning! I'm the oldest here!" 
- (To possessed Shin-Ah) "Tens, hundreds of times my heart has been pierced and my body has been torn apart. For hundreds, thousands of years I thought of erasing myself. I don't quite remember but, I also tore myself apart." 
- (To possessed Shin-Ah) "If it were something I could open, I would do it for you. But, I am a living monster." 
- (To possessed Shin-Ah) "It's because all of the other Dragons other than Zeno...are like Abi, Shuten, and Guen's children. I can't help but find you all endearing." 
- He ranked 8th in the character popularity poll conducted by Hana to Yume in December 2014. He scored 439 votes in total.
- Zeno seems to dislike getting teased for his age.
- In earlier chapters, Zeno's eye color was brown; however, in later chapters, it has been recolored to blue.
- Amongst the four dragons, he and Jae-Ha are the only known dragons who were known to be able to see the spirits of dead people.
- After the fact that he is capable of cooking was discovered by Yoon, he became the second chef of the group.
- In the past, Zeno has already gouged his eyes out but all that happened was they became "super-strong", but according to himself, his eyes were good, to begin with.
- It has been shown that Zeno can never lose the crest Hiryuu gave him. When he gave it away, it magically returned to him.
- Zeno is the one that adds "The Happy Hungry Bunch" to the name "The Dark Dragon and the Happy Hungry Bunch".
- According to Zeno, he can ride a horse while standing up.
- Zeno can juggle, as has been displayed multiple times when the group was posing as entertainers.
- Zeno has a tendency to refer to people as "Miss" and "Mister" with the exception of the dragon warriors, whom he calls by their title (ie. Hakuryuu, Seiryuu and Ryokuryuu).
- Zeno refers to himself in third person, a quirk he picked up from his now deceased wife, as a way to never forget his own name.
- Akatsuki no Yona Chapter 43, Page 7
- Akatsuki no Yona Volume 17
- Kusanagi Mizuho's Twitter
- Akatsuki no Yona Chapter 103, Page 6
- Akatsuki no Yona Chapter 102
- Akatsuki no Yona Chapter 101, Page 6
- Akatsuki no Yona Chapter 43, Page 3
- Akatsuki no Yona Chapter 43, Pages 15-17
- Akatsuki no Yona Chapter 62, Page 24
- Akatsuki no Yona Chapter 59, Page 14
- Akatsuki no Yona Chapter 101, Page 22
- Akatsuki no Yona Chapter 103, Page 18
- Akatsuki no Yona Chapter 103, Pages 6-7
- Akatsuki no Yona Chapter 103, Page 14
- Akatsuki no Yona Chapter 103, Page 19
- Akatsuki no Yona Chapter 101, Page 8
- Akatsuki no Yona Chapter 100, Page 21
- Akatsuki no Yona Chapter 42, Page 22
- Akatsuki no Yona Chapter 100, Pages 8-10
- Akatsuki no Yona Chapter 100, Pages 17-18
- Akatsuki no Yona Chapter 99, Page 30
- Akatsuki no Yona Chapter 42, Page 10
- Akatsuki no Yona Chapter 59, Page 13
- Akatsuki no Yona Chapter 62, Page 26
- Akatsuki no Yona Chapter 97, Pages 28-29
- Akatsuki no Yona Chapter 99, Page 32
- Akatsuki no Yona Chapter 100, Page 20
- Akatsuki no Yona Chapter 100, Page 27
- Akatsuki no Yona Extra Chapter 03, Page 7
- Akatsuki no Yona Chapter 101, Page 14
- Akatsuki no Yona Chapter 105, Page 4
- Akatsuki no Yona Chapter 180, Page 9
- Akatsuki no Yona Chapter 107, Page 27
- Akatsuki no Yona Chapter 107, Page 28
- Akatsuki no Yona Chapter 108, Page 16
- Hana to Yume (花とゆめ), 2015/1 edition
- Akatsuki no Yona Chapter 70, Page 10