SaGa Emerald Beyond - Tsunanori Mido vs. The Divine Fire Spirit 

Really boils down to some luck and appropriate turn management. Flowing Slash you generally want to prioritize as the go-to skill for the early turns while having people optimize what remaining BP you have to whittle down the adds and avoid enemy combos and Showstoppers whenever possible (Brusque Slice and Tackle for Delay if necessary). I didn't do the brutal fight in the first world so I don't know the exact specifics of what you need to do, but the advice here should be reliable enough to at least help out. Have fun getting into the SaGa series! It's a real treat once you figure things out!