A human girl was chosen as the fiancée to the prince of Dragonkin—she was supposed to be the "Mate." A heartbreaking love fantasy of a couple who were meant for each other.

Adeline, daughter of an earl, was offered an engagement from the Dragonkin Realm. They wanted her to be the "Mate" for the third prince. All Dragonkins have to find their "Mate" and take them to their castle built on the floating island and live together, although their lifespans might be different. Adeline was fragile... She could hear that everyone in the castle criticized her as someone not worth being the Mate to the prince. Even the prince himself seemed to hate her. She ended her miserable life by someone's poison.

Two hundred and fifty years later, Adeline is reborn in the same world. And again, she receives an invitation from the Dragonkin for a ball to find their Mate. She tries to run away... not knowing that there is a secret beyond this invitation.