I assumed the catch is the epic fantasy genre. If you mix guns with spells you essentially make swords pretty useless.
@Pyla8 Sure, there was the “oh guns don’t need skill” conception but the truth is, guns do require a fair amount of skill to use effectively (hence boot camp and sniper training). Anyone who has used a gun will tell you that hitting a moving target (especially in any of the vital organs) isn’t a cakewalk. Heck, some guns are heavy and have significant recoil. Those two factors can rule out individuals from using them.
I’d assume that when guns were introduced to military groups, their mechanics were thoroughly explained. Those Japanese swordsmen were likely strongly biased by their traditionalist values and likely didn’t pay much attention.
That said, I remember learning about how Maori (indigenous New Zealanders) picked up muskets from European settlers and engaged in inter-tribal warfare over territory. More than 18,500 people died from that (and the total population was only something like 60,000). It took a few years at most, but that was mostly because the muskets sold to them by settlers cost something like 200-300 potatoes (note: they were being financially exploited, it didn’t take that much to buy them). The price later dropped. After that, there was an “arms” race among tribes to buy muskets because they realised how effective they were.
Furthermore, those who prefer swords over bullets will face higher fatality rates. So even if they’re a relatively new invention, there will be more people who use firearms over blades very soon.
“The introduction of repeating firearms virtually ended the value of the sword as a military weapon, though isolated instances of its use continued in 20th-century wars. As it declined in its military usefulness, the sword gained a new role in the duel, especially in Europe, out of which practice emerged the modern sport of fencing.” Source: http://www.britannica.com/EBchecked/topic/577385/sword
I’m pretty sure most commanders would’ve realised that swords are pretty flimsy against guns. Anyone who stubbornly insisted on using swords probably would’ve been dismissed for tossing away lives. So, yes, swords were used for centuries - but for dueling.
About games, it’s pretty safe to assume they’re more focused on entertainment than complete historical accuracy. Especially AC - Ubisoft loves to work their visuals.