A Wizard's Secret - Chapter 3 - Supernatural Civilization

He became a teacher at the best magic academy in the empire.
….For being mistaken for someone else.

The youngest A-rank adventurer, child prodigy Kaizer, finds three babies who were the only survivor of a destroyed village. Then he decided to give up his job as an adventurer and raise them. Over time, the girls grow brightly and show exceptional talents in fencing, magic and management. However, these girls also seem to love their father, Kaiser!

Lucien, a guy who has nothing but the desire to save his mother. To get strong enough, he makes a contract with the demon of L.u.s.t. And now, only by making a great harem, will he gain the power to protect those dear to him.

As childhood sweethearts, they were made to engage under the manipulations of their families. It involved having to to live in the same room and sleep together.

One night, she is accidentally made drunk, and in his delirium, he kisses her only to realize he enjoys it. From time to time, he would sneak a kiss on her, but his “crime” is eventually discovered in an accident. After being accused by her, he says with a smile, “You are my wife, why can’t I kiss you?”

The two people’s daily routine is full of bickering and mutual discrediting of each other.

Although he claims to disparage, he actually cares intensely about her. He feels crazily jealous when she is close to other men, to the point of tying her to his side, so that she becomes exclusively his.

- Description from web