Enmei Ryu Shuriken were called Tanto Gata. These were either made from broken tanto or wakizashi blades.
Steel was also fashioned to look like they came from tanto. The tang was the main body of the shuriken with the remaining intact part of the blade as the blade of the shuriken.
The hole in the blade is where the mekugi hole was. This was the hole where a peg was inserted in a sword handle and passed through the tang.