The only reverse edged Japanese weapon/tool that I'm aware of is the KUBIKIRI or BOKUWARI. These were basically bonsai or gardening tools (although lots of fancy tales about them). I've only personally seen them in tanto size although I did see a pic of one on a sales site years ago in wakizashi length.
Might want to look at my page on unusual tanto for a kubikiri pic.
Rich S
-------------------------------------------------------
Richard Stein, PhD
"Old Puukkophile"
Japanese Sword Guide
http://home.earthlink.net/~steinrl/nihonto.htm
-------------------------------------------------------