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.[10] Since then, he has stopped aging and no longer hears the voice of God.[11]
He joined Gu-En, Abi and Shu-Ten, who were 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 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 were leaving.[12] 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 that time have come to know about his power and thought that he will no longer return anywhere.[13] During the time he was a priest, he solved the dangers coming to the country by his own.[14] Twenty years later, he sensed the fleeting life of Gu-En and he became depressed as he plead 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.[15] He had left the village he was born in, but he notes that it is still existing though it looks different than it used to be. Since he was stuck in his immortal body and did not have a village where he belonged to, he traveled around a lot and waited for King Hiryuu's reincarnation. At some point of his life, Zeno was married[4] though the specifics is still unknown.