Billionaire Assassin

*Warning! Warning!! Matured Content here! This book is rated 18+. Read at your own risk.*
To bring back his beloved dead wife to life, Demon has to kill and bring the souls of 16 Princesses to Hades.
He accidentally met Elena who happens to be his Dark Shadow Mate and when he discovered she was the last Princess he ought to kill.
Demon couldn't bring himself to do it and started protecting her from the others that wants Elena for the powers she didn't know she possess.
At the long run, Demon find out hi