Tidus, a troubled teenager living in Zanarkand, awakes in Spira to “Sir Jecht” in a monstrous whale costume. He tells him the world will end in 28 days, 6 hours, 42 minutes, and 12 seconds. At dawn, Tidus returns home to find his hometown destroyed. Rikku, a neighborhood al-Bhed girl, informs him not to mention he came from Zanarkand.
Tidus tells his psychotherapist, Lulu, about his continuing dreams about Jecht. Acting under Sin’s influence, he floods his school by damaging a water main. He also begins dating summoner Yuna, who has agreed to endure a pilgrimage to end Sin. Gym teacher Wakka blames the flooding on the al-Bhed. He begins teaching attitude lessons taken from motivational speaker Seymour. Tidus rebels against these motivational lessons, leading to friction between Wakka and Lulu.
Tidus asks his science teacher, Auron, about time travel after Auron brings up the topic. He’s received The Fayth of Time Travel, written by a senile woman urging those to stay away from the summoner.
Tidus eventually realizes his visions of Jecht are “daylight hallucinations”, symptomatic of paranoid schizophrenia. Tidus disrupts a speech given by Seymour by insulting him in front of the Spira. He then burns down a Yu Yevon Church house on instructions from Jecht. When the al-Bhed finds Spheres of Yuna the house’s remains, Yuna sends Seymour. During a hypnotherapy session, Tidus confesses his crimes to Lulu and says that Sir Jecht will soon kill someone.
Tidus and Yuna take the opportunity to throw a Halloween party to celebrate her not dying. Yuna arrives, distraught that Tidus has disappeared. Realizing that only hours remain before Sir Jecht’s prophesy, Tidus reappears and takes Yuna to seek the old woman. After telling him to stay away from the summoner, two Ronsos attack them. The fight spills into the street where Sin runs over Yuna, killing her. The driver turns out to be Sir Jecht, wearing the same monstrous whale costume of Tidus’ visions. Tidus shoots him in his eye with his Sir Jecht’s blitzball.
Tidus watches a wall of seawater forms above Zanarkand from above. Events of the previous 28 days recapitulate in reverse order and action until Tidus finds himself in a blitzball stadium. As he lays on the ground, waiting and laughing, the waves crash through Zanarkand, killing him.
Yuna rides by Zanarkand and learns of Tidus’ death from the old senile lady.
Yuna and Rikku exchange a glance and wave as if they know one another, but cannot remember from where.