Unlike his twin brother Akira who has a feminine-like appearance, Yui has a more masculine appearance. He has a black hair that reaches just above his shoulders. He has thick eyebrows which accents his intimidating aura. He wears a green fur hooded jacket. He also wears a fingerless gloves and wears black pants.
In the snow village of mount Iwanki, Him and his twin brother, Akira, were born. It has been said that a male Yuki-onna in their village is born once every hundred years. When growing up, the two would go near the barrier that protects the village but, kept getting caught. In a magazine Akira found on the mountain, he and his brother found about the Inugami detective agency and Tokyo.
When the women of the village are deciding which of the twins should be chief, Yui volunteered to be it as he didn't want Akira to suffer. As chief, he would have sex with the women to make sure the village survived. One day, his brother thought he had wet the bed and burned it as he didn't want the others to find out. This worried Yui as his brother didn't wet the bed but, has started ejaculating.
He asked the women of the village to let out of the barrier and promised them he would impregnate all of them if they accepted his request. They agreed and Yui talked to his brother as they are going near to the barrier. He told him that he was leaving the village too but, as they are getting close he left him. Before he was completely out of Akira's line of sight, he told him to go to Tokyo, find the kemono office, and they will see each other again.
Later, Yui would go to the place where it posses the Nil Calculus that created the barrier for the snow village to escape the women. He had enough and put the Calculus in him, wiping the village in the process. As the calculus possessed him, he only remembers what was important to him, his brother. Leaving in search of him and he was later reunited with him.
Powers & Abilities
Because Yui is a Yuki-onoko he posses the powers the species are known for.
- Cryokinesis: Yui has the power to control and create ice.
Yui's twin brother.
- His favorite foods are sweet things especially sweets topped with ice cream. 
- He has nothing in particular when it comes to his least favorite food. 
- The first thing he did when he came to Tokyo is to go on a sweets run.