The scene is happening in a park in Tokyo. Two friends talk about the meaning of life and the amazing longevity of the Japanese. A word is then launched: ikigai, which literally means "the joy of being always busy". According to the Japanese, we all had a character, a reason to exist, who pushed us to play every day and become actors in our lives. How do these "super centenarians" define their guide and what do they do on a daily basis? What are the habits to adopt to live better? In a book halfway between the guide and the testimony, the authors invite us to discover our own book to lead a long and harmonious life.