When four-year-old Kun meets his new baby sister, his world is turned upside down. Named Mirai (meaning "future"), the baby quickly wins the hearts of Kun's entire family. Kun becomes increasingly jealous of her, until one day he storms off into the garden, where he encounters strange guests from the past and future -- including his sister Mirai, as a teenager. Together, Kun and Mirai go on a journey through time and space, uncovering their family's incredible story, in this magical and emotionally soaring adventure about the ties that bring families together and make us who we are.