Yui (優衣) is a member of White Knights. She was the part of White Knights Squad No. 1.
Yui has short, dark brown hair. She is seen in her White Knights uniform and black high heeled shoes.
Yui is one of three most recent White Knight recruits. Their duties are to guard the church which covers the entrance to E.T.A.I.'s underground lair and helping Miyu capture more girls to increase their numbers. Like all White Knights, their combat abilities are of a level that can rival trained combatants like Aika or Risako.
She fights Aika with Misaki after Nanami is defeated, but is knocked out by an unseen blow after Aika decides to get serious. Though the details are unknown, we do hear her many desperate screams as Aika makes quick job of her. She is then shown falling to her knees, with her chest subsequently dropping to the ground and her panty-clad buttocks in the air.
When we next see her, Karen has moved her body and she is now lying flat on the floor, face down and legs spread. Her skirt rests over her butt, but it is so short it barely manages to cover it. Not happy with this, Karen hikes the skirt all the way up to the waist, to leave the ass fully exposed for proper examination.
Later, she, Misaki and Nanami are examined by Aika and Karen as the camera pans over their bodies from different angles. They are left lying there and are later retrieved by Miyu, who angry at their failure decides to demote them and keep them as captives insted of allies.