Ultra right-wing nationalists in Roppongi today. These are the guys who parade through the streets of Japanese cities in vans - often threatening black vans with tinted windows - pimped out with emperor-worshipping anti-foreigner nationalist slogans, blasting 1930s-era martial music at high decibels, and sometimes shouting militaristic slogans through roof-mounted loud speakers. They aren't prosecuted because letting them operate with impunity allows the government to boast about its free-speech credentials. I suspect they are somehow associated with yakuza criminal gangs. Often the yakuza present themselves as patriotic social clubs.
These guys were being followed by an unmarked police car. I know it was a police car because of the red strobe light in its windshield. The police were not interfering with them, though, just watching them.