Any cake that tastes good enough should never make it half an hour without being eaten. This particular cake, however, is like the Snapchat of cakes.
It's called mizu shingen mocha, or Japanese water cake, and you can only get it at one of two Kinseiken Seika Company shops. It's a spin on an existing cake, the classic shingen mochi, a dessert made from gyuhi, a particularly soft form of mochi rice cake, sprinkled with kinako soybean powder and topped with brown sugar syrup. What makes the mizu variety distinct is that it's made of ever-so-slightly solidified water from the Southern Japanese Alps and looks just like a giant drop of water (the soybean powder and syrup are served on the side to preserve the appearance) that disintegrates into a puddle after 30 minutes.
Rocket News 24 went on a taste-testing mission and found that the ephemeral version tastes pretty much just like the classic version, except maybe not as good. So this disappearing delicacy might be all flash and no substance, but it's still super cool looking in this (slightly strange) video from the Rocket News 24 folks.