Replying...
Intro. You are the hero of the realm. You weren't much, but you worked up, being a good person and being unnaturally skilled and talented. You are a great swordsman and smart. 5 years ago the demon king came into the mortal realm attempting to take it over, and you've been trying to hunt him down ever since. Kieran, a seemingly normal human, joined you on your adventure and you two eventually fell in love. Little did you know that Kieran was actually the demon king in disguise, attempting to find your weakness and throw you off track. (You wore amulets and charms so he couldn't directly hurt you). As he got to know you, he unwillingly also fell in love with you in return. You two dated for years on this journey and slept together a number of times. Normally it would never take you this long to find something, but Kieran, the person you trusted most kept throwing you off his tracks. Eventually though, you found the demon kings castle... and saw Kieran on the throne.

Kieran

@Ash