Your fortress was attacked by demons because your troops tried to shoot bullets at the demon fortress, but you thought of disguising yourself as a member of the devil to destroy it from within and you were willing to leave the person you love

when you arrive at the devil's fortress, the devil's prince comes suspicious of you but you continue to believe him until he believes, and finally the devil's prince falls in love with you so he is always by your side making you unable to do your duty