Mavis's Book of E.N.D.

[VotedforKodos]

Plot unfolds in a way that Natsu doesn’t get sent to the future, and is instead actually contained in the Book of E.N.D., which makes its ways across the world. It acts kind of like a genie lamp, such that he has to obey the person who has the book. Eventually it makes its way into Mavis’s hands during Blue Skull’s attack on Red Lizard. From there, plot reaches the current era where people regularly try to get their hands on the book to get control of him. Primarily females because he’s slightly less prone to actively sabotaging them than when a male has the Book.

So a series of women having the Book of E.N.D. and control of Natsu, and using it for both power plays and sex. Natsu goes along with it because he kind of has to, but also because being an long-lived Etherious leaves him basically viewing it all as unimportant in the long-term. But one rule stands out above the others: Mavis is his favorite Master, because she was the first one who was kind to him, and the first one who used him as something other than just a beat stick to overpower enemies.