The manga revolves around Sonoda Arisa and Uehara Tsubasa, twin sisters separated by their parents' divorce who promise to send letters to each other to keep in touch. They finally meet again for the first time after three years. Tsubasa is envious, but proud, of her sweet, popular sister, in comparison to her own school life where she if often referred to as "The Demon Princess" and Arisa suggests they switch places for a day. Tsubasa enjoys herself posing as Arisa and at the end of the day she finds a note addressed to her sister in her shoe locker. Arisa reveals that life isn't as happy for her as Tsubasa thinks and she pushes herself out of the window saying "You don't know their secret and you don't know my secret". The bushes manage to save her from death but she falls into a coma. Tsubasa reads the note she found for Arisa that reads "Arisa Sonoda is a traitor" and becomes determined to find out who is responsible for the note that may have led to her sister's attempted suicide. She continues to attend Arisa's school in her place to investigate.
Tsubasa Uehara (上原 つばさ Uehara Tsubasa?)
- A 15 year old delinquent who is known as a demon princess in her own school. The title character is her twin sister. She attends school in her sister's place in order to find out why Arisa tried to commit suicide. Tsubasa has purple eyes and blonde hair. She had the same color hair(darkish pink) as Arisa but later dyed it.
Arisa Sonoda (園田 ありさ Sonoda Arisa?)
- Tsubasa's twin sister and the opposite of Arisa. She is described as a sweet and kind girl. She was in a coma after she tried to jump out the window. She was known as the class representative. She was the former KING but after she went into coma, an unknown person took over her.
Akira Manabe (真鍋 明良 Manabe Akira?)
- A mysterious boy in Arisa's class. He is the only boy who doesn't get along with his classmates. Manabe has purple eyes and blondish tan hair. He eventually finds out that Tsuabsa had pretended to be Arisa to find out why she committed suicide and assists her in finding out who the new KING is.
- Tsubasa's close friend who helps her as she tries to figure out the mystery behind her sister's attempted suicide and the sinister things going on at the school.
Mariko Takagi (高木 毬子 Takagi Mariko?)
- Arisa's best friend. Normally cheerful and easy going. She also has a sinister and dark side. She had never been noticed by others until Arisa had become her friend and had done as KING told her to in order to get her Arisa back. She eventually transfers schools because she believes she is a nuisance to the class but Tsubasa tells her that she will always remember, believing this is what the real Arisa will say.
Midori Yamashita (山下 緑 Yamashita Midori?)
- Arisa's boyfriend. His is very kind and gentle to Arisa. However, he doesn't know that "Arisa" is in fact Tsubasa in disguise.
Chapters and volumes
</td></tr><tr style="text-align: center;"><td id="vol02">02</td></td><td> September 4, 2009</td><td>ISBN 978-4-06-364234-6</td><td>—</td><td>—</td></tr><tr style="vertical-align: top; border-bottom: 3px solid #CCF;"><td colspan="5">
</td></tr> <tr style="text-align: center;"><td id="vol03">03</td></td><td> December 25, 2009</td><td>ISBN 978-4-06-364246-9</td><td>—</td><td>—</td></tr> <tr style="text-align: center;"><td id="vol04">04</td></td><td> April 30, 2010</td><td>ISBN 978-4-06-364264-3</td><td>—</td><td>—</td></tr> </table>