Historically a lot of Japanese samurai (and other members of the bushi/warrior class) were huge fans of firearms. Japanese media and jidaigeki flicks often also have guns if the era is historically appropriate (anything set in the Sengoku era will have at least one character whose shtick is "gunslinger" if the cast herd is big enough) . Meanwhile...
*Stares at The Last Samurai and all the Western media portraying samurai viewing guns as dishonorable*
Nobunaga in particular was a huge fan of guns and pioneered the use of massed 'muskets' in Japanese warfare (he's not the first adopter, but the one most famous for it in Japanese history). Totally whupped the asses of the Takeda's expensive cavalry with them. So fictional depictions of Nobunaga will often show him using guns (or commanding musketeers) because that's what the historical figure was well known for (among other things).