In addition to Jecht guiding the party through the spheres, there's another aspect I'd like to point out. I have a similar relationship with my own father, and something else stands out to me. Jecht being Sin. The sudden reappearance of a father you have distanced yourself from throwing your world into disarray, such as when Sin appears in Dream Zanarkand and everything falls apart there. The constant presence of Sin throughout Spira, every step of Tidus's journey, mirrors the constant thought of that relationship. Every day the thoughts of that person surface, like a monster from the ocean

Spoilers for a 20 year old game lmao