Alba is reborn as the son of a poor nobleman. He is unable to use magic due to a disease and is destined to have a short life, so he is taken in by the duke's family. There, he meets Orsis, who was his “most favorite” in a previous life. The most favored person in my previous life is my brother-in-law? Such a life is too good to be true! But then he remembers that he is the cause of the loss of his beloved brother-in-law's smile, and begins to search for a way to live a long life in order not to lose his smile and to continue to love him.

He lectures his father-in-law, who has always had a hard time with Orsis, searches for medicinal herbs to cure his illness, and praises his brother, who has low self-esteem...

While Alba, who loves his brother, is running around desperately in such a way, Orsis is evolving into a little brother fool more and more! The story is about a man who is a little bit of a fool, but he's not a fool.