How can we live without Mozart's music? It has the power to change our lives and our view of the world. Mozart is a necessity. As children, we already listened to him, and this growing complicity lent itself particularly well to the game of dreaming. Who hasn't whispered to themselves, «What if...»? This is how we imagined Wolfgang travelling to Japan. This uchrony gave us the idea of combining our instruments with the koto, a traditional Japanese instrument, and uniting the two piano quartets with transcriptions of overtures from his operas and pieces written specifically for this project by two great Japanese composers. This journey offers an open view of a Japan so little known in Mozart's time, thanks to five imaginary letters written by the erudite and facetious writer Richard Collasse, author of the Dictionnaire amoureux du Japon and novels set in Japan. Finally, this strange odyssey bears witness to Mozart's infinite source of inspiration for artistic creation, with illustrations by Setsuko Klossowska de Rola and those made by her late husband, the painter Balthus, for the sets of Cosi fan tutte in 1959. What if Mozart had gone to Japan? Let's read and listen.