In the Wizrain Kingdom, a nation founded long ago by the legendary hero Vaide and his dragon partner Elnarfia, a young girl named Elna lives as the abused adopted daughter of the Caltzid baronial family. Her stepsister Laura and the baroness subject her to daily mistreatment, and she is treated little better than a servant. One day, after Laura throws water on her, Elna suddenly recovers the memories of her past life: she was Elnarfia, the great fire dragon who once protected the kingdom and carried the hero on her back. With the dragon's memories comes a profound shift in her perspective. Her human troubles no longer weigh on her, and she marvels at the novelty of having two legs and a human body, a form she had longed for in her previous life.

The kingdom follows an old tradition established by the first king: every year, all noble girls who have turned sixteen are gathered at the royal palace, because the hero Vaide once declared that Elnarfia would be reborn as a woman. The search for the dragon's reincarnation is a solemn royal affair. Elna is forced to attend alongside Laura, who has stolen a pendant containing a dragon scale that is actually a piece of Elna's former self. Laura presents the scale as her own and is mistakenly hailed as the dragon's reincarnation. At the palace, Elna comes face to face with the young king, Cross. In that instant, she recognizes him as the reincarnation of Vaide, the hero who was once her closest companion. Cross, however, shows no sign of remembering their shared past, and Elna decides to keep her identity hidden.

Laura and her parents attempt to exploit the false claim for political gain, but their scheme unravels when a rebellion attacks the palace. King Cross commands Laura to use her supposed dragon powers to crush the attackers, knowing full well she is a fraud. As the situation grows desperate, Elna steps forward and unleashes her fire magic, melting the rebels' weapons and armor in an instant. She tries to deny her true nature, but Cross, who had recognized her from the very first meeting, gently coaxes the truth from her. Elna confesses that her mother's bones were stolen and hidden by the baronial family, a grave crime in a kingdom where ancestral remains are held sacred. Cross is furious and promises to punish the family.

In the aftermath, Cross admits that he has always possessed his own memories of the past life. He had remained silent out of respect for Elna's wish to live as a human, orchestrating the false rebellion specifically to expose Laura's lie. Elna retrieves her mother's remains and buries them in the palace gardens. As the two speak openly for the first time, Elna reveals the deepest pain of her previous existence: after Vaide died, she lived on alone for centuries, clutching his bones until even they crumbled to dust. She had wanted to die with him. The forest spirits, hearing her wish, carried it to the gods, who granted her reincarnation as a human so she could find him again. Moved by her confession, Cross proposes to her, and the two become engaged.

Their new life together is tested by external threats. The Albarl Empire, learning of the dragon's reincarnation, launches an invasion. With Elna's power and Cross's strategy, they repel the attack and deepen their bond. Soon after, a delegation arrives from the neighboring kingdom of Marz, a former territory of Wizrain. The envoy, Kyle, is the reincarnation of Kalvis, the brilliant inventor who once fought alongside Elnarfia and Vaide. Unlike Cross, Kyle has no memory of his past life, and Elna must navigate the strange distance between a former comrade and a stranger who shares his face. At the same time, the emperor of Albarl demands that Elna be handed over as a condition for peace, leading to a tense diplomatic confrontation and a pursuit through the border mountains. In the struggle, Elna falls from a cliff, forcing Cross and his allies to mount a desperate rescue.

Through these trials, Elna gradually learns to let go of her attachment to the past and embrace her human present. Her role shifts from that of a lonely dragon guarding a kingdom from afar to a woman who can live and love alongside her reincarnated partner, finding meaning not in eternal vigil but in shared mortal days.