Ok, the title might be slightly misleading, but there is still a Japan-link.
So, pufferfish. Specifically, a wikipedia entry called Pufferfish mating ritual.
Long story short, one particular species of pufferfish make complex geometric circles in the sand to attract a mate. And this particular species is found only in Japan.
It's beautiful. It's bizarre. And it's absolutely amazing.
From the wikipedia entry: In a 2014 documentary by the BBC, narrator David Attenborough describes pufferfish as "dull, almost to the point of invisibility. But to compensate, he is probably nature's greatest artist."
Cracks me up.