That shit was called Hachigane and in time it became a symbol of good luck among warriors, because one saving your life from a blow to the head meant you had incredibly good luck.
And let's keep it up with weeb war history. One thing usually people say about samurais is that they didn't used guns because they considered dishonorable. Instead, they didn't used guns because of several reasons: they could only fire once before becoming completely useless, clumsy and loud, the shot could be deflected by armor, very expensive to produce and you couldn't use them while raining. This meant that not many warlords in the Sengoku era didn't adopted them once they got introduced by the Portuguese in Japan (the portuguese also introduced bread and two sweets that they are known today in Japan as Castella and Confeito). It wasn't until some rowdy and westaboo feudal lord decided to make use of those guns. It was Nobunaga Oda who showed everyone that guns were a very powerful weapon if used in the right way when he managed to defeat the unbeatable cavalry of the clan Takeda with several squads of riflemen. Thanks to him other feudal lords and warlords started to implement guns and also the use of the Ashigaru (translated means "Light foot"). The Ashigaru were super light infantry, usually peasants levied from towns which were considered not more than cannon fodder in past times since they were only used as spearwalls agains cavalry. With the introduction of guns, weapons that are easy to use with minimal training, the Ashigaru gained a lot of notoriety and they were levied in massive numbers during the Sengoku period due to their newfound usefulness in battle.
That's the battle at Nagashino which essentially oversaw the eventual the destruction of the Takeda clans power in feudal Japan. The battle was by no means remarkable in the fact that the Daimyo had been employing Teppo Ashigaru and firearms in battles before that point.
What set apart Nobunaga's forces is that he'd had stockades built to protect the handgunners from the cavalry charges, had implemented strategies for continous firing which the men had drilled in (3 guns to a man, with a reloader for continues fire in volleys.) It was then that the other Daimyo saw how effective proper placement and use of firearms could be used to take down a superior fighting force. (Takeda had the best heavy cavalrymen in Japan.)
The irony of the Ashigaru being given firearms, came from the fact that the Portuguese who had been trading the arquebuses to the Japanese Daimyo, had essentially been selling them older and outdated designs, which had a small but usually lethal failure rate. Ashigaru were seen as a perfect medium for this system, as levied peasants dying from exploding long guns wasn't seen as a great waste of man power, where as a trained Samurai was.
Also the dislike for the matchlocks as being dishonorable didn't come about until much later during the Tokugawa period, and for the same reasons that the French disliked English Bowmen at Agincourt, it was seemingly unreasonable to the Bushi class that a peasant armed with a flintlock/matchlock with minimal training could take down a Samurai who had spent his whole life training in the variety of weapons systems that made up the bulk of learning throughout their career.
It also served the purposes of the Bakufu in trying to consolidate the power of the Tokugawa. By denigrating the use of firearms, as well as increasingly isolating the ability to trade with outside forces, as well as the development of some very strict travel restrictions, the chances of peasant/ronin/rebel uprisings was kept to a minimum.
The Shimbara Rebellion led by Amakusa Shiro was the catalyst for the Tokugawa Bakufu to start this, as the Christian's who had rebelled against the government had been armed principally with arquebuses, and had managed to hold of a prolonged siege by the Shogun.