Gravija is percentage based, meaning that it takes off 75% of a character's current HP. Therefore, it alone cannot kill anyone, as it cannot reduce a person's HP below 1.
However, the "final battle" is so laughably easy that you could probably beat Yu Yevon with a wet rag. I've statted Yu Yevon under the assumption that it's actually a fair fight, which (in the game) it's not, due to the collective fayth of Spira casting Auto-Life on the entire party. The only way to lose is to somehow get your whole party petrified.
I have found pics online that should fit the bill.