My Younger Childhood Friend has Bound Me, and is Unwilling to Release Me!

Ayu Sato (27) has a childhood friend, Yusuke Kotori (19), who is eight years younger.
Yu is a young and famous novelist, but his vitality is 0 compared to his work.
Ayu loves Yu like her real younger brother, and she often takes care of her.

One day she was asked by Yu to be "tied up?" As an interview for his novel …
It's a childhood friend of a mediocre office lady and a younger boy.