JP Wikipedia: http://ja.wikipedia.org/wiki/LOST_CHILD
Official site: http://web.archive.org/web/20081209104227/www.tama-soft.com/products/lost_child/
VNDB: http://vndb.org/v1183
Getchu: http://www.getchu.com/soft.phtml?id=29267
It's a kind of old VN that I hoped to read from few years back
As far as I know, the story centers a young boy named Shouji Tokitou. One day he was attacked by a mysterious monster and saved by a girl named Ai. She then transform Shouji to an Amitto to fight the monster...
phew.
The VN has gameplay too, BTW
Anyone interested?