First you must have required tools :
-CheatEngine 6.0 : http://adf.ly/1XaL7
-Opera : http://adf.ly/1YWcP
FireFox / Chrome / IE
Step By Step:
(1). Open Ninja-Saga : http://apps.facebook.com/ninja-saga/
(2). Go to Kage Room
(3). Choose the Mission
(4). Open Cheat'Engine 6.0
(5). Change Value type : Text
(6). Scan the Mission that you play ( Ex : Mission_104 )
(7). You got 1 Address, Click on the Red Arrow (Red Cursor on CheatEngine)
(8). Change the Value ( ex: "Mission_104" to "Mission_108" ( 108 : Kanesada)
(9). Finnished the Mission, and you'll got Kanesada Weapon.