In an ideal language, one phoneme has one equivalent grapheme and everyone is happy. English doesn't have that due to the weird way it evolved. Mostly due to French influence. If you look into the history of English, you'll see that Old English is pretty straightforward in that regard, it's in Middle English where things start to get messed up (keep in mind neither Old English or Middle English refers to what most people refer to as "Old English", as then they usually mean Shakespearean English, which is actually Early Contemporary English).

That said, Tidus's name is not of English origin, therefore, English phono tactic rules do not apply. You don't pronounce Czech as "see-zek".