Majutsu-shi no noroi

Natsuko has been on the run for most of her life, a specialist type of Nen user--an Elemental--she is constantly hunted down, used and abused for her unique power.
On the verge of death, she is found by an eccentric and blood-lusty man who calls himself "The Magician".
From there, her life twists and turns in ways she never thought possible.

If you're looking for pure smut you can check--
Chapter 6
Chapter 7
Chapter 10
Chapter 13
Chapter 15
Chapter 16

Note: Set in the HunterxHunter universe 8 years after the cessation of the anime. All characters with the exception of Natsuko are NOT of my own imagination and I give full credit to Togashi Yoshihiro for their creation and licensing.