Mitari Yo is a career woman who has successfully advanced in her career working for a shoemaker, but her relationships keep failing resulting in a constant broken heart. Her best friend and former classmate from high school and university, Ishida Ren who works for a developer, is the only person who understands her and that she can confide in. On Yo's 29th birthday, they both 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 30. They've always said that it would be impossible for them to fall in love with each other, but with the appearance of Ren's company junior and Yo's ex-boyfriend, the two start to rethink their relationship.