In Final Fantasy X, Yuna meets Tidus during her pilgrimage. Tidus is upbeat and carefree.
In Final Fantasy X-2, Yuna encounters Shuyin who’s:
spirit was corrupted with negative feelings of failing to protect Lenne and hatred for those responsible as he was forced to endlessly relive the memory of his death. Shuyin lost his sanity and became driven by fantasies of revenge against all of Spira.
But as the players note, similarities exist between the two. And the lore of the game supports a connection.
Tidus is the incorrect memory of Shuyin. We find out that Tidus is a “Dream of the Fayth”, in which he was “ordered into existence after the original Zanarkand was destroyed”. The fayth
are humans who willingly had their souls sealed in statues in a state of dreaming in Final Fantasy X. Their powers allow a summoner to coalesce the power of pyreflies to create physical forms from the fayth’s dream, called aeons, or other magical phenomena.
But as they dream, they have to recreate their memories on something. Thus some fans speculate that Tidus is based on someone: Shuyin.
Evidence comes from Final Fantasy X-2, in which Maechen implies Shuyin’s resemblance to Tidus is more than coincidental. This has lead fans to speculate
the fayth summoning Dream Zanarkand “dreamed” Tidus in an attempt to recreate what they remembered of Shuyin, as they were charged with remembering and preserving every aspect of the destroyed city.
Fans note the similarities between the two. Tidus “has disheveled blond hair with spiky layers”; same with Shuyin, who also “has shoulder-length disheveled blond hair and blue eyes”. Both wear a similar style of dress, whereas Shuyin’s look more complete. The only difference is the personality, as Tidus is noticeably more friendly than Shuyin.
Refutation also comes Final Fantasy X-2, but this time the International + Last Mission Ulmania, which:
posits that Dream Zanarkand was created as the ideal representation of the original Zanarkand, a wish given form. Since the original Zanarkand was the model for everything in Dream Zanarkand, this extended to its inhabitants, who would marry one another and have children, continuing the cycle of life. Thus the genes of the dream’s inhabitants blended to form a unique populace. According to this it is unlikely Shuyin is the direct model for Tidus, as Dream Zanarkand’s Shuyin should have lived a millennium ago. It is possible, however, that Tidus is a descendant of Dream Zanarkand’s Shuyin.