I'll add Ellone's theme as Eaglegun suggested then.

Maybe I'm a Lion only plays once during a boss fight and I feel it references Griever more than Squall. The Oath plays during Squall's speeches to the Balamb Garden as well as when he rescues Rinoa from being frozen. To me I feel it resonates with him more.

Any thoughts from VIII fans about Seifer? Premonition is more associated as Edea/Ultimecia's boss theme so I was wondering if anyone had another suggestion.