I Became the Sea Guardian’s Adopted Daughter

“You said you wanted me to become the Duke’s bride at the age of five?”
Nassia, who used to be an archmage, was reincarnated with an incurable disease.
I thought that I’d be abused after getting sold off in marriage to a Duke who was said to be cold blooded, but he suddenly suggested for me to become his adopted daughter!
I accepted it rashly in order to gain strength and escape, but it turns out that all mages in this world are given the death penalty?!
What if I get caught?
All of a sudden, I was left to conceal and suffer with a big secret.
“You can trust me, Nassia. Most of the things you fear won’t happen.”
They all said that he was a terrifyingly cold-blooded man, so why are you being so nice to me?
The healing romance fantasy of Ain, a reliable but clumsy father, and Nassia, who finds it awkward to trust people!