The sun had gone to bed a long time ago and Rin had most certainly not noticed. He'd been in the classified section of one of Konoha's dozen libraries doing research. The classified kind of research, the kinjutsu kind. The kind where you had to know half a dozen codes to be able to read the scrolls in the first place, not to mention how to bypass or disarm the traps just to get them off the shelves.
A little known fact: one of the perks of being an jounin was the upgrade to your library card. Hell, you probably needed to be one to avoid getting killed in the reference section. Still, Rin was - y'know - a geek, and nothing was going to keep him away from books. Not that he was still running around pulling down new ones, for the past two hours he'd been making his own notations on materials he'd pulled out and replaced soon as he was done.
Now he was sitting alone in the empty room, nose in a book that weighed more than he had til he turned eleven, researching the mundane - a history of summoning contracts. The classified books had been about kinjutsu, but now he was looking into the background specifics of his own personal research. Things like cellular cohesion, metalurgy, physics of velocity and friction. Rin had been looking up specific facts on all of those topics and more and making notes in his own coded shorthand. He was tired, but he was going places. And anyway, this was important.
And he was happy. This was something he loved to do, which was part of why he was good at it (the other part was him being a genius, but that didn't make it fun). The only downside was... he had that tendency to completely lose track of time and what with the library being considered a secure site it didn't have windows to show how late it was.
Two in the morning and he was on to his second notebook, sketching a diagram of chakra paths, humming contentedly, pushing his glasses up his nose, and completely in his own little world.