Sure, he could argue at this point that this whole space had become his library too, but unfortunately, he was still stuck on studying the decaying surface of the diary in his hands.
He didn't even have to open it to know what happened next: how, once they had reached Atlantis, the people were so wary of these strange visitors (and rightfully so), and yet there had been the kind Princess Kida, who gladly welcomed them into their city. But her parents, the King and Queen, were also greatly suspicious of their visitation, thinking their visit an omen---
Xigbar's---no, Luxu's---prediction about Rourke had been correct, and the cruel man had brought the Darkness with him---and with that Darkness, the suffering, tragedy, and death that nearly swallowed the city.
And even though, in the end, the Light of the Princess had prevailed, the Darkness had still touched the innocence of the land---and Luxu had not prevented it, even though he had had his own share of suspicions. And yet, he ignored it---chose to believe that he had to be wrong, and that everyone venturing toward Atlantis was good, and that he was simply being foolish.
There rose in Xigbar, burbling in the pit of his being, something that he had sought to shove down---to never allow it to touch him again. That he had shed it after all these centuries, that it was all behind him---
He realized his grip on the book was tight enough to cause the already tattered leather to crack further---and he forced himself to thrust it back onto the bookshelf, the movement sloppy and unfocused, wedging it between two other books before snatching his hand away.
Xigbar didn't hate---had been able to push that emotion down, too---but he hated, now, the loss of his composure. The way his chest expanded, then was forced to let out a deep sigh---
But, perhaps, despite these slips, he could still right himself---just enough. Just enough.
"Dude sounds like a sentimental sap. Makin' choices based on his emotions, all willy-nilly," and he turned his back entirely to Aqua, throwing out an exaggerated shrug. "Anyway, it's probably not even an actual diary---just some old novel that's like a fake autobiography. People do that sometimes."
Then, most definitely regaining his balance (at least, he was sure he was), "C'mon, there's way more interesting stuff in here, anyway. I know ya got some books about, like, lascivious pirates or whatever, yeah?"
Xigbar began meandering back toward the other end of the library---still refusing to look at Aqua.