Kun is a happy four year old boy until the birth of his little sister Mirai. His joy quickly turns to disappointment when she replaces him as the center of attention. But Kun discovers a mysterious garden : a magical door to a fantastic world where past and future meet. There, he will encounter his family members at di erent stages of their lives, including his baby sister as a teenager. These experiences change his vision of the the world and help him grow into the big brother he was meant to be.