Takes place before Part 1 - Chapter 4...
After wandering around the ruined castle for some time, Xehanort finally found the once royal library, but like the rest of the castle, it was in near ruins; parts of the ceiling were crumbled onto the floor, book littered in large piles, and the vines from before growing all throughout the castle goes without saying. Xehanort began searching the shelves for anything of interest, but found nothing. Just before he gave up, he came across a tome labeled, "Dangerous Threats To Equestria", and with a sneer, he plucked it off the shelf and began researching.
"Hmm...'Discord'...'King Sombra'...'Tirek'...'Changelings'...'Nightmare Moon'..." he read off the names he found, the latter's backstory reminding him of Riku when he gave in to darkness and a certain feckless youth who became his new vessel, then he saw a subject within that piqued his curiosity, "...'Tartarus; a prison for the worst criminals in Equestrian history'..." he sneered once again, and his eyes then laid upon an open book with blank pages inside it, "Hmm...perhaps I should chronicle my findings..." he looked back at the tome in his hand, "I suppose even a utopian world like this has its dark corners..." he chuckled darkly at thought of having multiple candidates for his Seekers of Darkness.