She is a 1st year middle school student.

~! It is later revealed she is from 2006. !~

Kokoro is a junior high school student who doesn’t fit in at school and has secluded herself in her room. One day, the mirror in her room begins to suddenly shine and she is sucked inside. There, she finds a fairy tale castle and six unknown junior high students. Then a girl wearing a wolf mask appears and tells the seven of them that they have been chosen to have any one wish they want granted. Why were they chosen? What do the seven of them have in common? What is the wish that they each hold but can’t tell anyone about? When all is revealed, a miracle beyond their wildest dreams awaits.
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(Source: Tokyo Otaku Mode)

Kokoro is a junior high school student—but after years of bullying, she’s become so anxious that she no longer goes to school. One day, she’s pulled through her full-length mirror into a castle in another dimension by a girl in a wolf mask. The mysterious girl tells Kokoro and six other kids that they are all competing in a scavenger hunt. If one of them finds a key that unlocks a secret room, that person will get one wish granted. As long as they observe the rules of the world, they can come and go as they please. The seven kids gradually grow closer as they explore the castle, but the scavenger hunt is never far from anyone’s mind. After all, only one of them can win and receive their heart’s desire.
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(Source: Seven Seas Entertainment)

Kokoro Anzai