Zen is came from Yakushi Clan and a childhood friend of Rikuo where he later become his sworn brother.
Zen is originally from Yakushi Clan. He also a childhood friend of Rikuo Nura and consider him as his own brother. He can use poisonous feathers for combat. Although he has a poor health. He also became a sworn brother of Rikuo after he save him from Hibedayu with his Yokai form.
Zen was created by Hiroshi Shiibashi. He was first appeared on Manga, Act #3. Later on the Anime, he appeared on Episode #2. He was voiced by Tomokazu Sugita.
Zen is a Yokai who joined the Nura Clan and a sworn brother of Rikuo Nura. He has a khaki scruffy hair that turned black at the neck. He had red eyes. He wore a dark blue robe over a purple kimono dress.
As a Yokai, Zen is a very loyal Yokai to Rikuo and always willing to fight alongside him. He don't usually like Rikuo as a human, especially when he sees him befriends with humans. Although as the story progressed, Zen started to go along with any Rikuo's decisions.
Zen decided to visit the Nura Household to talk about Rikuo on becoming the 3rd Heir of the clan. Rikuo has disappointed and angered Zen as he said he don't have any intention of becoming one at all. When Zen and his subordinate Hebidayu is leaving the Nura Clan's house, they headed back to Yakuzen Hall.
On the way, Zen's condition has worsen. Shortly after that, Hebidayu betrayed Zen and attacked him in sudden. Rikuo chased after them in Oboro-Guruma. Rikuo came and tries to explain everything to Zen as he turn into his Night Form. After his transformation, he manage to defeat Hebidayu and saved Zen.
After Hebidayu's defeat, Zen decided to do the Exchange Loyalty Cup with Rikuo as a sworn brother.