Mitari Yo is a career woman who works for a shoe company. She finds her work rewarding and has successfully advanced in her career. Her love life, on the other hand, isn't doing as well. Ishida Ren works for a real estate developer and is Yo's best friend. An ex-classmate from both high school and university days, he understands her best and is the only person she pours her heart out to. On Yo's 29th birthday, the two friends place a wager to give 300,000 yen as a congratulatory gift to the one who is the first to get married by the last day they are both 30. Although they declare that it is impossible for them to fall in love with each other, this wager, as well as advances by Ren's junior in the company and Yo's reunion with her ex-boyfriend, lead to gradual changes in the relationship of the two best friends.