Thanks for the info Toua
Makura Soft's page for the game:
http://www.makura-soft.com/h2o/index.htm
Getchu's page for the game:
http://www.getchu.com/soft.phtml?id=236105
And finally the official site for the
Shigofumi ~Stories of Last Letter~ anime has opened:
http://www.shigofumi.jp/
Shigofumi ~Stories of Last Letter~ is also a light novel series from the boy's label
Dengeki Bunko (a light novel label from MediaWorks aiming at teenage boys/young adult men).