Taka and Miki have been together since their school days and are now married. Their "mutual friend," Yui, is the same Yui as them and is still single and unmarried. She is a working woman honing her career in the publishing industry. They are just friends and sometimes she comes to the couple's house after work to drink with them. Both Taka and Yui have a "comfortable friendship where we don't have to worry about each other." Then, one night, when Taka's wife Miki goes out to stay the night, Yui comes to visit...