Jūmonji Yari image - Bushido: Legend of the Samurai

Early yari are believed to have been derived from Chinese spears, these hoko yari are thought to be from the Nara period (710-794) and while they were present in early Japan's history, the term Yari appeared for the first time in written sources in 1334 but this type of spear did not become popular until the late 1400s. The original warfare of the bushi was not a thing for "commoners"; it was a ritualized combat usually between two warriors who would challenge each other via horseback archery. However, the attempted Mongol invasions of Japan in 1274 and 1281 changed Japanese weaponry and warfare. The Mongol-employed Chinese and Korean footmen wielded long pikes, fought in tight formation, and moved in large units to stave off cavalry. Polearms (including Naginata and Yari) were of much greater military use than swords, due to their much greater range, their lesser weight per unit length (though overall a polearm would be fairly hefty), and their great piercing ability. Swords in a full battle situation were therefore relegated to emergency sidearm status from the Heian through the Muromachi periods. Around the latter half of the sixteenth century, ashigaru holding pikes (Nagae Yari) with length of 4.5 to 6.5 m (15 to 20 feet) became the main forces in armies. They formed lines, combined with arquebusiers and short spearmen.

Jūmonji yari (十文字槍), cross-shaped spear, also called magari yari (曲槍, curved spear), looked something similar to a trident or partisan and brandished a pair of curved blades around its central lance. Occasionally called maga yari in modern weaponry texts.

(Source: Wikipedia)

Bushido will feature several variations of Yari types such as the Kamayari, Tsuki Yari, Kikuchi Yair and Fukuro Yari.