Yuuki Oku is one of the seven at the Institution. He has blueish-black hair and violet eyes. He wears the normal uniform given to everyone at the Institution. Yuuki is known for being the main character (MC) of the manga "Dolls Code".
Yuuki was put into Institution for unknown reasons. He is however, believed by the other criminals as the puppet.
Yuuki Oku came from a single-parent family, as his father left his mother. One day, when Yuuki Oku came back home, his mother was crying and when he asked what was wrong, his mother asked if he loves her or not and kissed him.
Time went by with his mother and him having a relationship, Yuuki Oku could not take it anymore and said that a mother should not do such things. His mother, who has an unstable mind, took a knife and tried to kill him as she wanted Yuuki Oku all to herself. Yuuki Oku trying to protect himself, somehow killed his mother which was the crime.