Calm
From Final Fantasy Wiki
In Final Fantasy X, the Calm is the unset amount of time of peace that follow when a summoner defeats Sin, dying and posthumously becoming a High Summoner in doing so. Sin would inevitably return later on however, at which point summoners would defeat Sin again, repeating the "spiral of death" indefinitely. When Tidus first learns of this, he wonders why anyone would fight Sin if it always comes back, but Yuna convinces him that doing so is worth it. The Eternal Calm came when Yuna was able to defeat Sin for good, bringing peace to Spira.
