In Final Fantasy X, Yuna’s ultimate weapon is called Nirvana.
Nirvana is Yuna’s Celestial Weapon, the strongest weapon associated with her character. It is obtained through the Monster Arena side quest: after capturing the required fiends from the Besaid region, the player receives the weapon from the Monster Arena owner. Its full potential is unlocked with the Moon Crest and Moon Sigil.
The weapon’s name reflects Yuna’s role as a summoner and the game’s spiritual vocabulary. Final Fantasy X is set in Spira, a world shaped by the teachings of Yevon, the recurring threat of Sin, and the passage of souls to the Farplane. Yuna’s journey initially follows the traditional summoner’s pilgrimage, though she and her guardians ultimately reject the sacrificial cycle behind the Final Aeon.
Nirvana is commonly confused with other famous Final Fantasy weapons. World Champion is Wakka’s Celestial Weapon, Masamune is associated with Auron, and Save the Queen appears as a weapon name in several entries. The Moon Crest is not enough by itself to maximize Nirvana; the Moon Sigil is also required.