The overall shape and geometry of a Japanese sword is named the sugata. While the sugata Shinogi zukuri (diamond shape) is the most common by far, also unokubi zukuri has gathered a large amount of followers.
The term unokubi (???) literally means 'neck of the Cormorant' which refers to the tapering of the monouchi (area from the tip to around 15 cm downwards the blade; the point of impact) while leaving the kissaki shape intact. Blades with an unokubi zukuri sugata often also feature naginata-hi which is a short bo-hi with a diagonal termination.
This geometry was initially designed to lighten the blade of a naginata while keeping most functionality intact. Remember that the effective force / momentum of a naginata is pretty high due to its impressive length. Winning 100 grams on the steel can be the difference whether the weapon can or cannot be handled.
Anyway, somewhere in history the unokubi zukuri geometry was also passed on to its cousins; the katana, wakizashi and tanto.
In the picture you'll see a modern made Unokubi zukuri katana made by Kaneie Sword Art. On this earth (brown) themed sword you will find a Botan themed fuchigashira and a bamboo leaves tsuba. The handle has been wrapped with Japanese brown leather.
More pictures on our website:http://www.thesamuraiworkshop.com/EN/catalogue/swords/menkyo-collection/cha-botan-unokubi-zukuri-katana/shop_mode=product_detail&product_id=425