Mahoutsukai no Konyakusha (LN) (Novel)
Other Name: Fiancée of the Wizard / 魔法使いの婚約者

Genre: novel, Drama, Fantasy, Psychological, Romance, Shoujo
Country: Japan
Author: Nakamura Shuri
Year: 2015
Chapter: 7 Volumes (Ongoing)
Related story:

Summary:
I who was reincarnated into a world of sword and magic. The revived Demon King, the Hero chosen by the holy sword in the middle of that unfolding common fantasy trope, the position bestowed upon me was to be the magician’s fiancée.