PACHINKO!
One hundred yen would get you a handful of shiny ball bearings which you would try and translate into a whole lot more by getting them into the winning slots and multiplying your investment. The centre of the console is the main target and get that to open up and it's like heaven. Watch video below to get a bit of the vibe.
After you fill up a bucket or two - if you're lucky (and skillful) - you would go to reception and exchange them for some prizes - or if you are in the know; lighter flints. Take these little plastic packs around the corner to a concealed tiny window and get some yen in exchange. Casssshhhiiinnnggg!!