Even an anthole may collapse an embankment.— Japanese saying
Consisting of light polearm infantry, Naginata Ashigaru may not be as good as the Southern European Espadachines, yet their main draw lies in several areas: firstly, they can be recruited one age earlier than the Armoured Militia which are recruited by China, Hungary, Mongolia and Turkey. The second is that like most polearms units, they also can inflict brutal amounts of splash damage if left alone to their own devices. Lastly, their fairly cheap cost means that although weaker than most other factions' medium infantry, you can create massive numbers of these units to bulk up your numbers and to assist your costlier albeit stronger samurai units.
Although the common perception of Japanese and foreigner alike often assumes that the samurai (or also saburai) were the lynchpin of Japanese military might, it was actually the humbler ashigaru which formed the rank and file of pre-Tokugawa Japanese armies. The ashigaru were originally infantry levies (mostly armed with bows) recruited wherever possible to make up numbers where the bushi or samurai classes were deficient, but as the size and intensity of wars in Japan increased, so did their importance - by the early modern era, ashigaru were often trained semi-professional warriors armed and salaried by the local strongman who recruited them to do his bidding.