Hetare Onna Maou no Irekawari

The Female Demon King Isabel is feared as the strongest class of demon, but she dreamed of meeting the human prince who promised to marry her when she was a child, and she waited patiently for that moment in the demon world until she became an adult. However, when she turned 16, she learned the truth: the prince, Samuel, already had a fiancée. Although she made up her mind to step aside for the sake of the prince's happiness, she wanted to see him again, so she invoked a "curse" technique to switch the body and soul of Lily, his fiancée. Isabel succeeds in switching their bodies, but is shocked to find that Lily's body is sicklier and weaker than she expected, and she also learns that Samuel's fiancée is not Lily...?