Ah, of course. 'Protect the summoner, even at the cost of one's life'. The Code of the Guardian.
In Final Fantasy X, a guardian (ガード, Gādo?, lit. Guard) is a warrior tasked with protecting a summoner during their pilgrimage across Spira to defeat Sin and bring the Calm. Most summoners travel with one or two guardians, though some, most notably Yuna, are protected by many more.
Guardians are the only individuals allowed to accompany a summoner into a Chamber of the Fayth. If anyone else does so, the summoner may face sanctions as strong as excommunication from Yevon, even if they did so without the summoner's knowledge or consent.
The concept of a summoner's guardian is based on the first summoner to defeat Sin, Yunalesca, who was protected by her husband, Lord Zaon. After the formation of the church of Yevon summoners being protected by a guardian as per Yunalesca and Zaon's example was adopted as doctrine. Another duty of the guardian is to offer themselves as the fayth for the Final Summoning to calm Sin, and ultimately become the next incarnation of Sin, although it this is often unknown to the summoners and their guardians prior to their meeting of the unsent Yunalesca in the Zanarkand Dome.
- The term "guardian" is written in all-capital on one of Tidus's sword models in Spiran script.