To be fair, that dude is literally Guts and, while I am not super familiar with Berserk, doesn't he also kill gods? 🤔
It's funny he's one of the guys I only struggled with the second time through because my first time I was using an ash of war that knocked his ass down and could just keep him on the floor the whole fight. The second time I didn't and he doesn't stun easily lol
He also made all the other mausoleum fights seem easy, since they all can be stunned with just R1s or R2s.
If you have a greataxe, you can just lightspam him to death. He can trade with you, and you will lose any trade, but if you do it right, the greataxe can effectively stunlock him.