I guess R.Scott or Douglas watched Out of the Past + The Yakuza !

Even The Yakuza karaoke scene or the fliperama games, the furtive entrance of the American and Japanese partners to the Yakuza's house, the use of the shotgun, the good-bye salute at the airport... were all repeated in a different way in Black Rain. Michael Douglas wore a big leather jacket reminiscing of the big jackets worn by Mitchum in noir films (like that one with Kirk Douglas called Out of the Past and even The Yakuza itself). In Out of the Past , Michael Douglas'dad, Kirk, played with Bob Mitchum.
Ken Takakura works in both films. Black Rain and The Yakuza. The only thing missing was Kirk Douglas wearing a black robe with a dragon and eating rice in an Asian saloon as he did in the western called The War Wagon!
May I have to remind you Robert Mitchum was always in Riddley Scott's mind for his Deckart character in Blade Runner and he had to give up the idea of letting Harrison Ford to wear a hat otherwise he would've been too much alike Indiana Jones wearing a Fedora hat????

There's a thin gap between skepticism and cynicism