13. Werewolves of London – Remus Lupin/Sirius Black
Werewolves, much like other large predators have territories, and as they are human for most of the month their territories are usually arranged around their human lives. Mates, homes, families, which for Remus was 12 Grimmauld Place and Sirius.
Even in human form Remus couldn't quite keep the territorial feelings down, he'd taken to greeting every person to arrive at HQ, as if to warn them about moving in on his territory, Sirius was quite amused by that.
He'd also been rather amused when Remus would glare at everyone who came within two feet of him.
It turns out that Sirius was also being rather spectacularly dense in that while he was amused by everything Remus was doing, it took him several weeks to realise exactly why he was doing it. Well to be fair it actually took Remus jumping him in the hallway for his to realise, but all's well that ends well.