Yuuka

Yuka is a physician of Messiah and secretly, a spy working for the 'Alliance'.

Personality
Yuka was once a happy woman until the death of her husband due to Arcadia's fall radically changed her. In present, she was now a wicked woman who solely desired vengeance upon those who wronged her. Yuka would manipulate, undermine and murder anyone to accomplish her goals. While undercover as Messiah's physician, she presented herself as a kind and concern woman.

Background
Yuka lived in Arcadia with her husband who was one of Arcadia's scientists that produced Japan's First Knight. Tragedy struck however when the First Knight went on a rampage due to Akira Nishino's experimentations resulting in countless deaths, including Yuka's husband. Yuka held her husband as he died.

Years later, Yuka joined a group called the Alliance who tasked her to infiltrate Messiah and sabotaged the group alongside their mole, Yudai Saejima so that they could claim their base as their own. Having successfully infiltrated Messiah, Yuka learned to her outrage that not only Akira Nishino was still conducting his experiments but Akane Nishino, the First Knight had forgotten what happened to Arcadia. Yuka spent her time getting close to Akane all the while secretly planning her revenge against her.

Revenge against the Nishino Family
When Akane brought back two survivors, a boy named Cid and a girl named Natsume, from a Magical Beast nest, Yuka did her best in taking care of them them. She would explained to Cid about the Magical Beasts and their nests, believing he had lost much of his memories. While tending to Natsume, Yuka found her watch was missing but concluded that it must have fallen off.

After a Magical Beast stampede was stopped by the Black Knight, Yuka eliminated Yudai Saejima per the Alliance's orders but the woman took advantage of the man's death to further her own goals of revenge. She cut Yudai to pieces with a chainsaw and framed the death as Akane's doing. When Yuka provided Akane the "evidence", Akane went into a nervous breakdown until Yuka sedated her and took her away to tend to her. Unbeknownst to Messiah, Yuka actually kidnapped Akane.

Yuka meet up with Cid who revealed proof of Akane's innocence. Worried that the boy will discover the truth, Yuka secretly ordered two hitmen to take Cid out. During another Magical Beast stampede, Yuka took the chance to find Akira Nishino and killed him along with Natsume. She took the Brute's head that Akira wanted to use. Yuka coldly stated down at Akira, telling him that she hoped his death will hurt.

Death
Having escaped Messiah, Yuka returned to the spot where she had kept the unconscious Akane Nishino. Suddenly, she was confronted by Minoru who deduced her as the Alliance spy. Yuka explained her past and intentions to Minoru before injecting Akane with the Brute's blood. With Akane now transformed into her First Knight state, Yuka allowed herself to be killed at the First Knight's hands. Despite nearing her end, Yuka hugged the First Knight before laughing, having finally gotten her revenge.

Powers & Abilities
Yuka was just an ordinary human with no magical abilities whatsoever. However, being Messiah's physician, it can be assumed she knew medicine. She was also a skilled spy, capable of infiltration the human refuge without anyone deducing her true identity until it was too late.

Trivia

 * Yuuka can be considered the second female villain, the first being Reina Oriana.