The back of the blade (mune) is a characteristic feature of a sword blade. Samurai swords have this one:

Mune Hikushi
Blunt-angled

Mune Takashi
acute-angled

Mitsu Mune or Shin No Mune
Double ridge

Maru Mune or So No Mune
Round

Hira Mune or Kaku Mune
Flat
Source: "Das Samuraischwert", published by Ordonnanz-Verlag in 2004
You can find more interesting articles about other components of the samurai sword in our article category Components of the samurai sword.