Damn it, John beat me to it! I had a feeling it was the equipment issue and the guard blocking your path.
When I bought Ys IV in late '96, it was the first all Japanese RPG I would be attempting to play. I knew there was a good chance I'd get stuck, but I justified buying it because I fell in love with the prior ones and I knew the soundtrack would be killer so I'd get that benefit at least, minus not understanding the story. Sure enough I got stuck where Superplay did, this damn guard that wouldn't move, yet I knew I somehow had to get him out of the way, that he was blocking in-game progress. I had to give up for a couple of years, sadly...
This was '97 now, I was on a 56kbps modem at best, had bought my first Windows 95-based PC same year as Ys IV, yadda yadda, Internet was still taking off, I was working on my CS bachelor's, there was nothing I could do, I gave up. Many years later though I learned about game guides being online and I remembered about getting stuck in Ys IV, so it occurred to me to search to see if there was one on Ys IV. Sure enough I found one, and it clearly stated all you had to do was equip your 1st level sword, shield, armor, as the idea behind that was because this was the equipment you stole from the castle earlier in the game when Karma breaks you out of jail.
I avoided using any guide again, and did finally beat it, in Japanese and all. That was a happy day, albeit something I'd have to wait years to see.
It was as every bit as great as the others and I kept my fondness of it even leading up the the point of the translation project! Now other bastards get to enjoy it for the first time fully in English unlike what us pioneers went through...