A human girl and The devil's son(On Hold)

Lucy is warned that if she walked out on the first full moon of the summer and said a phrase of words that you demon would appear the next day, and he would make you fall in love the first time you see him or saves you
Natsu is the devil's son he was brought to earth when a certain girl said a phrase that makes a demon fall for their human girl, and he has to make her his in a year, he must try everything in the book to make her his before the year is over or he must stay on earth until the end of her days
But the question is will he fell, will she fell, or will they except their love for each other and live in Hell or Earth?
choose wisely or face the consequences