I'm writing this review primarily in response to the previous review, which asks why this module has so many dependencies.
The answer to that is the the Japanese calendar is basically the Chinese calendar plus a system of eras based on the current emperor. The Chinese calendar is rather ridiculously complicated, requiring all sorts of fun calculations of the position of the moon.
Unsurprisingly, this leads to needing lots of code to do this math. Daisuke wisely chose to put this code into various utility modules, rather than jamming it all in the Chinese or Japanese calendar distro, since this stuff is generally useful.
Then some doofus comes along and complains about this, saying "why not recode it in a simpler way" as if Daisuke could just magically hand-wave away all the math and still make it work. Awesome.