Revision control system
As of recently, Hikou no mizu switched from the tuxfamily-hosted subversion repository to a gitlab-hosted git repository.
You will find it at the following link:
Former subversion repo
Hikou no mizu uses subversion as revision control system,
you can use it to grab or contribute to a development version.
Here is the path to the repository ! :-)
If you like, you can explore it online using ViewVC or WebSVN :