The embryonic form of samurai is the military attache under the legal system of heian period, Japan, which was originally established by Emperor Wu Hengtian of Japan to consolidate the political power. Before the Heian period, all able-bodied men except slaves had the responsibility and obligation to become the targets of emperor soldiers. However, these soldiers have to supply themselves and support themselves, so many people can't return to their hometowns, but choose to settle in the local area. People can be exempted from military service by paying heavy taxes. This kind of soldiers, mainly farmers, are collectively called defensive soldiers in Japan. Because of the nonstandard defensive soldiers and the huge burden of farmers, they were abolished by Wu Heng in the early period of Ping 'an. This form of soldier is not a real soldier.

In the early days of heian period (from the end of the 8th century to the beginning of the 9th century), Emperor Wu Heng wanted to consolidate and expand his rule in the northern part of Honshu Island. The crusade army sent by the Emperor against the Amish people in northern Honshu lacked morale and discipline, so it was difficult to win on the battlefield. So Emperor Wu Heng began to seek help from local tycoons, and proposed that he would award the title of General Fighting for Foreign Countries to any local forces that replaced him in the Crusades in northern Honshu. These skilled local tyrants soon became the tools used by the emperor to crush the resistance.

The firearm you are talking about should be an iron cannon. Iron cannon was used as a battlefield weapon after it was introduced to Japan in the early days of Antu Taoshan. Although many samurai used iron guns at that time, it was usually not a samurai regiment but a low-level infantry class called "light iron guns"