Magic.

Songkrod and Auerkarn were a loving couple but then the bad guys killed Songkrod's family and kidnapped him. Auerkarn is sad that he’s gone. She's a doctor now but has not moved on from Songkrod. Songkrod returns after being trained and brainwashed by the bad guys, he identifies as Kim now. He came back to use magic to get revenge. When Auerkarn met Kim, she was confused because he looks like her former lover but he acts very differently. They slowly start to fall in love again.