
SPOILERS -
OK, so I read all the chapters again. Suu's mothertongue is the one of the sacred books. He lived in the desert with his teacher. He can read the sacred books written in the old tongue. So what was in that book that the prince asked for? Suu seemed startled by it but he forgot his memories afterwards.
And how is this mothertongue useful for the dragon's rain? It seems deeply related.
Sahara told him that he needed food, and Suu was there. But it really because Suu is Suu as Sahara stated it, that he can be used as food. So why is that?
My god I love this story so many mysteries

Aaand I thought about that book again.
After Suu read, he was ill, cured by the prince, with some memory loss on the side. Only thing that remains is the fact that he kept blabbering the word 'run' in his mothertongue. So WTF was in that book?!
The 'run' word was not linked to the fact of knowing the Dragon identity, or else he would have dreamed it other times too, it is linked to the content of that book. The prince doesn't know that Suu can read it. And he wanted to retrieve that specific book. He asked Suu to do it because he thought he couldn't read it. So what is the content of that book that made Suu want to run?!
She is soooo damn CUTE!