Spoilers for all games below
* Akiyama's safe. Ignoring the fact that Akiyama just having 100 billion yen lying around (which honestly trivializes the 10 billion yen incident to me, but that's another thing)... there's the fact that he had a safe. With 100 billion yen in cash. That he locks with... oh wait. He doesn't lock it. There's a button to open it behind a conspicuous book on his shelf. The plot was set into motion by the fact that someone had wandered into his office (which, by the way, was unlocked), picked the book off the shelf (because it was a conspicuous book) and completely by accident found the money. Honestly, it borders on IdiotPlot for me... which seems harsh, but there's no reason that should have happened. Akiyama would have been better stuffing his money into a mattress.
* Tatsuya, street fighter, prize fighter and petty thug. But yet he still has time for silly part time jobs like serving Gelato at a frilly gelato store, a fast food worker and a doorman for a hostess club. Why can't Tatsuya get a real criminal job like picking pockets or helping run extortion rackets?