I'm assuming you mean Yusha? Yeah he's supposed to be ridiculously hard. It's been a year so maybe there's no point in hiding it anymore (IF ANYBODY DOESN'T WANNA GET SPOILED DON'T READ THIS THO) But he doesn't have much control of the sword's power, so the trick is getting him stunned or paralyzed while charging up his super attack. If you do that, he will lose control and the attack will backfire ;)
And aww <3 Thank you. This game has a pretty special place in my heart too, so it makes me really happy to hear this.
I still have some drafts for a follow-up questline, but it's been forever and I'm probably not returning to this project anytime soon, if ever. The story is complete as is tho, so I think it's fine to leave it to rest and move on.
Either way, I'm glad you've had a good time with it, and it helped you get into more similar games! xD