Putting My Life on the Line, I Go All-in on Luck Enhancement

A brief description of the manga The Archmage’s Restaurant:

A man who was reincarnated in another world as a 9th class wizard and retired after saving the continent from a dragon war. He decides to open a small restaurant in the countryside, but his routine is anything but ordinary.

On the second floor of his restaurant, there lives a black dragon who has transformed into a woman, named Rurin. She is greedy, cute and loyal to him, but also ignorant and clueless about the human world. They live a fun and warm life, serving customers, solving problems and growing violets in the garden.