I've always been interested in the existence of Sengoku Jidai era firearms. I think this comes from watching James Michener's Shogun miniseries a bunch as a kid. And to think that it didn't jade me for life!
Really though, much of the remaining interest and spur for research was the game Shogun: Total War. Anyone who has ever played it, and used Musketeers to mow down whole rows of Heavy Cavalry knows what I am talking about.
Because Medieval: Total War would not run on my computer, I was forced to install the more obsolete Shogun, and thus the revival of interest in the subject. I found these two great illustration of what the poster says is Samurai firing Teppo. They honestly look like Ashigaru to me, but I'm certainly no expert, and I know that Ashigaru actually were the lowest class of Samurai at one point or another, so it's not as clear cut as you would think.