The Japanese blade has been made in a large variety of shapes and sizes over the last 1,300 years or so. The Sugata or overall form is the first thing to be considered when appraising a blade. Shown below are the main typical forms and cross-sections which have occurred. It is important to note however, that these typical shapes can and do vary in every dimension to a greater or lesser extent throughout the history of Nihontô.
This type of blade form and cross-section can be seen in tantô and ko wakizashi in all periods
This type, with a 'shinogi' line on each side is an ancient form found around the end of the Heian period
This form is Hira Zukuri on one side, and Kiri Ha Zukuri on the other. The form originated at the end of the Kamakura period (1288-1334 CE). It was again popular at the beginning and at the end of the Edo period (1596-1643 & 1781-1867 CE)
This form has a sharp edge on both sides of the blade. It was used for tantô after the middle of the Muromachi period (i.e. from around 1467). It occasionally occurs with sori
This is the form of blade which occurs most often in all periods after the Heian. It's defining features are that it has a shinogi closer to the mune (back edge) than the ha (sharp edge), it has sori (curvature), and it has a yokote (dividing line marking the start of the tip or kissaki)
This form is similar to shinogi zukuri, except that it has no yokote. It is found most often in the Muromachi period, most frequently on tantô and wakizashi
This very ancient type, with a blade which changes cross-section about one third of the distance from the tip, originated at the end of the Nara period (708 - 781 CE). It is also known as kogarasu maru zukuri after a famous sword called the Kogarasu Maru (Little Crow) which is attributed the the smith Amakuni
This type is most often seen in blades from Yamato province, and in schools deriving from Yamato since the Kamakura period
This form (known as 'Cormorant's Neck') is similar to kanmuri otoshi zukuri except that the shinogi ji slopes sharply to the mune in the central part of the blade, having much less of a slope in the kissaki and machi areas (see lower diagram which is a top view of the mune). This form also frequently occurs without a yokote.
This type with an extremely large kissaki is a rare form originated by Shimada Sukemune in the late Muromachi period. It is known as Osoraku (Japanese for 'perhaps') because this word is carved on the original blade.