Hi Guest127 !
Thank you for your warm thanks addressed to me and those who help me translate the novel.
About the story, there are lots of things people don't understand.
In fact, Nojima wrote the novel in a very particular way.
He crossed the relation between Kush and Valm, and the one between Tidus and Yuna, and when you understand that, you understand why Nojima wrote the novel like it is right now.
I did not found about it before reading the novel a second time, but then it all appeared clear to me.
Once you discover that, you will find out that Ifahnal has in fact killed Tidus, with this (too) famous blitzball bomb, and that he planned this before Tidus and Yuna washed up on the island.
I will give one hint to help you understand : Tidus and Yuna end up in the ocean because their boat has been destroyed. But did you try to find out what caused this ? If you read the novel correctly, you will find out that Tidus smells gunpowder before fainting. Does he ring a bell to you ? Don't you remember a similar scene somewhere else in the novel ? Yeah, Valm did exactly the same as Tidus while he was with Kush in some kind of appartment and that an enemy made a blitball explode. So what then caused the boat of Tidus and Yuna to be destroyed ? I think you know the rest
There are other parallels like this one in the novel, and they make you understand what exactly happens.
I'll let you find them, but feel free to ask, I'm all open to answer you.
The only part I don't still quite understand is why Ifahnal could not send Kush away. My theory is that he was not able to know where Kush was, and that he used the love relation between Tidus and Yuna, similar to the one between Valm and Kush (a love between a summoner and her guardian), to make them find the location of Kush, with the help of Tidus power.
Anyway, still waiting for my lovely FFX-3 !