http://variety.com/2017/film/global...-discusses-next-project-exclusive-1202429514/
Much more at the link.
Bonus:
Mirai follows a 4-year old boy who is struggling to cope with the arrival of a little sister in the family, until things turn magical. A mysterious garden in the backyard of the boys home becomes a gateway allowing the child to travel in time and encounter his mother as a little girl, his great-grandfather as a young man and his sister has a grown woman. These fantasy-filled adventures allow the child to change his perspective and help him become the big brother he was meant to be.
What is the genesis of Mirai?
There is a common thread in the themes of my films: The Girl Who Leapt Through Time was about youth, Summer Wars was about family, Wolf Children, Ame and Yuki were about motherhood, The Boy and The Beast was about the father, and my new film is about the relationship between brothers and sisters. Mirai is about a boy who is trying to reclaim the love of his parents.
How personal is this new project, Mirai?
If I decided to tell the story of a brother and sister, its because after the birth of my second child, our eldest one got the impression that this newly arrived baby stole her parents, which made her ferociously jealous. I understood then what humans fundamentally desire, what they thirst for. Its my childs jealousy that gave me the idea to do this film.
Much more at the link.
Bonus:
From a Western point of view, the time in-between the storyboard and the completed film is so short in Japan.
This is due to the auteur policy that centralizes the power in the hands of the director. The director typically researches and thinks as much as he/she can during the writing phase of the storyboard, and then tries to be pragmatic when the film goes into production.