
Lavi wasn't always the Librarian. In fact, when he was first brought here, he was a victim of the books just like everyone else. He survived most of the mishaps that kept happening though, even began to thrive in the Lirbaritorium. It was while he was exploring the place and learning as much as he could about the Library that he ran into the former Librarian, Yuu Kanda.
He'd already been in the Libraritorium for a month before he ran into the Librarian. Both were very surprised by the encounter and it actually turned into a fight. He later found out that Librarian Yuu had some kind of connection with the books, and as a result, he usually knew when someone was brought to the Library. Finding out that the books hadn't alerted him to Lavi's presence both surprised and alarmed him. Lavi, on the other hand, had thought he'd been alone in this place. He was even more surprised than Yuu that someone was here. The fight between them lasted some time and was eventually called to a halt, both claiming it was a draw. Lavi found Yuu interesting and started following him around. What amused and fascinated him the most was that Yuu seemed to have some power over the books as well. He quickly forced found a place under Librarian Yuu's wing, coercing begging him to teach him everything he knew. The closer they grew and the more he taught him, the more Lavi began to monopolize Yuu's time and energy. He took over his duty of greeting the first arrivals, making the introduction short and sweet so he could spend more time with Yuu. He even started trying to take over his book duty, though Yuu resisted.
Lavi knew he was being selfish but he wanted Yuu all to himself. Ten years had passed in this fashion, both of them struggling to maintain a balance in their relationship and working in the Library. Finally, Lavi got Yuu to relent. He could deal with the books much faster than Yuu could, leaving them more time to spend together. As he started taking over Librarian Yuu's book duties, he pushed for more in their relationship. He knew Yuu liked him; it was easy to read it on his face. He was a terrible liar. He stole a kiss from Yuu, and then he stole more kisses. He wanted to completely dominate him. Unfortunately, what he didn't realize was that the books didn't like what he was doing. Yuu tried to warn him, tried to explain to him that he had to be the Librarian, but Lavi wouldn't listen. They both paid for that mistake.
They had know each other for nearly twenty years before Librarian Yuu was attacked by one of the regulars. The only reason he wasn't killed was because the man opened a book and sucked him inside. He was severely injured and there was blood everywhere. When the man tried to enter the book after Librarian Yuu, he found he couldn't. The books were protecting him. Unfortunately for the man, Lavi happened to stumble across him while he was covered in blood, cursing that he couldn't finish off the Librarian. In a rare fit of rage, Lavi killed the man. The books lent him their help and his death was the first and only one where someone didn't revive in the Libraritorium. Lavi, having lost the Librarian Yuu, went mad for a bit. He ignored the few friends and regulars that had come through over the years. He begged and pleaded with the books for them to return Yuu but nothing ever happened. Eventually, he gave up asking and then, one day, he found something had changed.
He had a name tag.
He was the new Librarian. He lost all hope of Librarian Yuu ever returning after that. He went back to talking and laughing with their friends and the regulars of the Library but he was never the same. There was a distance now that could be felt. A piece of his heart had been closed off to the world. Nearly a forty years past and all their friends had disappeared over time, returning to the worlds and lives they originally came from. He spent another sixty years alone before the newcomers began showing up again. By that time, he'd been so used to being on his own that he couldn't bring himself to embrace them whole-heartedly as he had once been taught to.
What he doesn't know, what he hasn't realized however, is that the new comers only started arriving again because Librarian Yuu was finally released from the book. He no longer appears as he once did, though... And he's taking great pains to avoid running into Lavi, so there's little chance of him finding out any time soon--unless an incident occurs. Unfortunately for him, the books seem to have been appeased and want the two to meet.