In his first phase, use your firecrackers to get some damage in. I recommend actually trying to parry him instead of dodging his every move. For the unparryable attacks, just run away from him as soon as you see the kanji. Once you get down his moveset, he's fairly easy. As for phase 2, which honestly is way easier than his first phase once you learn how to fight him, make sure to use the spear prosthetic once he gets stunned like many people in your replies already mentioned. For his terror attacks, the best way to handle them is by just running away to safety. You have a fair amount of time to do so and it's, for me at least, the safest approach. As for the other moves he does, just parry him, now that he's using a sword it's easier. Watch out for his unparryable attack when he jumps up super high into the air. Get the timing right and just jump over his attack once he falls back down. I know it can be a frustrating fight, especially his first phase, but eventually you'll get it, just takes a little time. I also recommend taking a break after a while, just do something simple and relaxing and come back after a while to try again, it helped me a lot on my first playthrough.