Braskas final aeon is actually luck based in NSG (with restrictions... you can use an aeon and 3 hits its dead or use trio of 9999, blitz ace attack reels and its dead.) due to the sword delaying your entire party as well as hitting them to. In the first phase you basically prep your party to survive and then going for the kill. At 60,000HP or less in the second phase is when he changes his overdrive and you will die if you see it, so we need to skip it entirely, this where Tidus' talk ability comes in and you get 2 free turns. Also at this time his sword move goes up from 33% to 67% so you want to hope that if you cant do 60,000 damage he dosent do that to often.... I got lucky.