Yui is a young woman with long hair that reaches to her lower back with bangs styled in a straight Hime cut.
She wears what appears to be a well dressed School uniform.
Yui's personality is unknown, but she seems to be calm and mature.
After the battle with Shinpaku and YOMI had ended, She and Hyōgo and her master and fellow disciple left for Big Lock to attempt to rescue Diego and Alexander. After his Master returned without them, they realized they would not come out and when his master didn't respond as to why, they note he's as strict as ever
Later, Kajima Satomi introduced her and her partner to the rest of YOMI (minus Chikage and Lugh) and when Hyōgo pointed out there all weak without weapons, he says he was joking trying to get inside there heads. However, Rachel took offense to this and tried to attack him as she warned him and watched as he cut Rachel's clothes.
She was later seen with the rest of the Yomi unarmed and armed divisions training for battle and remained quite when Hyōgo tried to calm everyone else down. She was present when Kajima stepped in to lead them to battle. She was later seen with the rest of YOMI (minus Kajima) facing the Shinpaku Alliance. After Kenichi, Miu and Niijima escape, she and the other disciples charge the Shinpaku Alliance.
As the battle progresses, Chikage runs towards Ukita's direction and he prepares to fight but she simply runs past him and heads towards Thor's direction. She kicks Thor behind his knee causing him to lose balance and giving the female kodachi disciple an opening to stab Thor in the thigh.
As the battle progresses, Hyougo stabs Thor on the shoulder and Siegfried comes to his aid but ends up being slash by Hyōgo's fellow kodachi disciple. Before the attack lands Chikage rushes through the battlefiled and throws the fighters attacking Ukita and Hyōgo. Hyōgo is forced on the defensive by Bersker's attacks as his fellow kodachi disciple backs him up but she is forced away by Hermit.
Once she and the others are at the disadvantage, she and the other armed disciples work together as they fight the Shinpaku and YOMI forces as Chin Sougaku (crescent moon spade) and Ortal Sin (jamadhar).
- The name Yui means "tie, bind" (結).
- Yui's surname Sayama means "cramped, narrow, contract, tight" (狭) (sa) and "mountain, hill" (山) (yama).