Movie producer/novelist Genki Kawamura became the first Japanese to win Best Director for his movie, A Hundred Flowers, at the 70th San Sebastian International Film Festival in Spain.

A Hundred Flowers is about a son and his mother who suffers from dementia. Despite the mother's fleeting memories, certain images of his son remain.

"Every time she loses her memory, I regain love," says the son in the trailer.

Released in Japan on 9 September, the movie features prominent actors Mieko Harada as Yuriko Kasai, the mother, and Masaki Suda as Izumi Kasai the son.

It marks Kawamura's first directorial feature, adapted from his novel of the same name, and dedicated to his grandmother who suffered from the same illness.

"I want to tell my grandmother in heaven of this joy," Kawamura, 43, told the media.

He recalled the movie was challenging, since he wanted long takes in a single shot, and quick flashbacks between each scene.

"When I spoke to my grandmother, she would be talking about one thing, then suddenly switching to another topic, like the weather changing. I wanted that same level of humanity, of reality," Kawamura said.

He was drinking wine at a bar in Bilbao, Northern Spain, when he received a call informing him of his winning the San Sebastian award. He "almost spat out" his drink, he told the audience upon receiving his trophy.

Kawamura debuted as an author in 2012 with the novel If Cats Disappeared from the World, which has sold over a million copies in Japan and has been translated in 11 languages worldwide.

His production credits include the movie Confessions and the award-winning anime Your Name.

San Sebastian is regarded as one of the major international film festivals. The top three are Cannes, Venice, and Berlin.