Throw Weapon Technique?!

Hi yall, I started this game a couple days ago, I’m only on the path to the old couple in the swamp in chapter 1. I looked up a walkthrough in order to find out how to get to the chest under the hill of rock in the cave immediately after the first balloon shop (still don’t know how to get it, he completely ignored it in the walkthrough so if you have info on that I’d appreciate it too) and in the walkthrough the guy is using the throw weapon technique I saw in the demo. wtf?! Is there like a ng+ type deal or did I totally miss out on this core ability?! Is there any way to backtrack and get it again if I did miss the chest? Right now all I have technique wise is the upper cut (also in that cave) and backstep. I was real upset because I almost missed backstep too, which is so mandatory. Why are all these core moveset abilities in chests when I can’t go back to these areas, stresses me out lol. Anyway thanks guys for any help you can give, I am learning that there is not a lot of info about this game online, at least not in English. Cheers!