"A dream come true"
Yakusho, 67, told NHK the award was nothing short of "a dream come true" and credited director Wim Wenders for his understanding of Japanese culture and customs that he said helped to make the film, set in Tokyo, such a success.
He also spoke of his belief in, and commitment to, Japanese cinema. "I would like to continue to work on Japanese films. Directors such as Koreeda Hirokazu are receiving high acclaim, and I believe that the Asian film industry will become stronger if we work together. That's something I'd like to be involved in," he said after the May 27 awards ceremony.
Yakusho is the first Japanese person to win Best Actor at Cannes since Yagira Yuya in 2004 for true-life drama Nobody Knows, but it wasn't his first taste of victory at the festival.
He played the lead role in 1997's Palme d'Or winner The Eel, directed by Imamura Shohei, and accepted the top award on behalf on Imamura, who had already left.
That was, he says, an inspirational experience: "I was touched by the event's enthusiasm and fervor, and felt the power of film."
The film Perfect Days is set in Shibuya, Tokyo. Yakusho plays a toilet cleaner in a story that gradually reveals the man's background and inner feelings.
"The man I played, Hirayama, has seen hell in the past, and I think the audience saw my performance as a way of wishing him a good luck in his new life," the actor said.
Yakusho's rich list of credits
Born in the southwestern prefecture of Nagasaki in 1956, Yakusho began his acting career as a member of Mumeijuku, a group led by actor Nakadai Tatsuya. He gained attention for his role as Oda Nobunaga in NHK's 1983 historical drama Tokugawa Ieyasu.
Yakusho starred in the 1996 hit romantic comedy Shall we Dance? for which he picked up multiple Japanese acting awards. In 2009, he directed for the first time, and played the lead role in Toad's Oil.
Scriptwriting honor for Monster
Monster was veteran director Koreeda's 7th film to be nominated in competition at Cannes. It came away with the screenplay award for scriptwriter Sakamoto.
Sakamoto appeared at a news conference in Tokyo on Monday alongside Koreeda. He said he felt the award carries responsibility rather than joy, describing the prize as "a burden I have to carry."
"I wrote the screenplay thinking about those who live a lonely life somewhere in the world, and believing that they will come to understand the heart of the story," he explained.
The film centers around an incident stemming from a quarrel between elementary school students. The story is told from the conflicting viewpoints of a parent, teachers and others, encouraging viewers to question who or what the "monster" really is.
Sakamoto said he would be pleased to work with Koreeda again, if offered the chance. "I respect Koreeda both as a director and a screenwriter," he said.
Koreeda himself put together a new team to make Monster, noting: "I am always happy when I receive compliments on my cast and staff."
The latest honors reflect the depth and strength of Japanese film talent that enjoys a storied history at Cannes.