I showed him a particular immigration document issued to me that he is not, strictly speaking, allowed to ask for prior to starting a custodial interrogation. He then started second guessing Immigration's decision to offer me a visa.

That was good news, since it convinced a colleague he was overstepping his authority. I was released 5 minutes later, with an admonition to lock up my bike properly to avoid the scourge of foreign bike thieves plaguing Ogaki.