I cannot beat the boss that uses the sword.

You can always grind a few levels out, before facing him, maybe do some quests for extra items. Sometimes get decent gear or materials for better gear, through those.

Food items are tops, this time around. Found pizza and steak were 2 of the best, for me, if a tad pricey in gold.

Wait so where do I get the Katana weapon to parry?

Can I parry him with my other weapons?

Is there a tutorial in game that teaches me how to parry?

This is my first time hearing about parry in this game.

Also, how do I parry once I get the Katana?

I easily beat him on hard after 3 or 4 tries. I used the spell that summon a drilling sword in front of you. (I might stop using it now, way too powerful haha) Everytime he went into his stance to counter you, I just used the spell on his foot and held it there, for an average of 5 or 6 hits that does 20+ damage. Just dont try to get to close, only hit him once or twice while you jump over him or go under him when he jumps. Good luck! Oh and for healing I used an early game quest reward that gives you 3 Uni Bowl Rice, or something like that. That food fully heals you!

Double tap right then attack while holding a nodachi you can see any techs you learned in the pause menu after you use them once. The bookcases spread throughout the game will tell you the inputs for various weapon skills and what weapons you need to learn them but you can also just experiment to find them.

I haven't been able to beat him in over 3 hours of trying. JUST HIM for 3 hours (and I guess the one enemy between him and the save room).

I was surprised when I didn't beat him the second time. At the third time I stopped messing around and actually tried to avoid his attacks. He just has a lot more HP than I expected. I'm not the leik uber pro, but I've never had this much trouble with a boss in any metroidvania Castlvania except for maybe a couple of the bosses of the game.

have you tried the hidden bosses? those are the real shit man, i can get over most bosses by spamming skills, but not those hidden ones.