This is a tantô for the Samurai of modest means. Hidden in the bottom of the saya is a removable wooden block. When taken out, it reveals a chamber for hidden coins. I say modest means, because I was able to fit only three Ichibu gin and three Isshu gin in the compartment. Not enough money to get the Samurai in any kind of serious trouble, but certainly enough to get him one heck of a night on the town and probably in a lot of trouble with his wife.
