Ashigaru regiments are composed from not very disciplined human warriors, armed mostly with long spears, bows or very poor quality arquebuses. Their equipment is usually very basic and rudimentary. These corps are made up of peasants, mostly reluctant to follow the Samurai to war, but many have no choice. Though not especially strong or skilled, the Ashigaru make up the bulk of Nippon's armies. When the presence of the samurai is required to fight in different battles, they will take a large part of these troops with them, although they will also place a part in their castles, in case the peasants need any kind of help during their march. In periods of peace, the Ashigaru carry out routine tasks, such as guarding the boundaries and patrolling the Oni lands.
You can learn more about the Nippon the Oni shogunate fan project here: https://www.worldanvil.com/w/warhammer-fan-concept3A-nippon-the-oni-shogunate-danilagi7