Just don't try to beat him via guarding and crits? His main attack seems like a pretty obvious message to me.
I'm stuck on the third one. The second isn't so bad but the third is a bitch and half.
Yea, I beat the first guy spamming the silver sword special attack, feel kind of dumb now; he just makes it so you can't fight the same way you've been going up until now. The second guy wasn't anything special, can be beaten using normal tactics. The third one is kind of annoying, you can get him with 2 critical hits though. His "Preparing" buff is a guard it seems like. The fourth one uses magical attacks so it's best to unequip the Catgirl's Ring if you have it, but beyond that he's just strong; has 75 HP and hits like a truck. I beat him by using both buffs from Maply and Jadk and then drinking an energy potion at the start of the fight to insta-crit him and then fought normally after that. He's the last fight you have to do, your fifth opponent is Lutvrog and you don't even get a chance to fight him proper because he's so much stronger than Sabia, it's just text. You get the best result of the arena by getting to him though.
Edit: It occurs to me as I re-read the text that you probably have to have both fought him with a handicap and won and trained with him alone as well as with both him and Neve to have the best result from your "fight" with him. The description makes mention of all 3 events.