They were running down a corridor, they didn't have a clue which one, trying to get to charms. Suddenly, they bumped into a young boy in their year, nocking him, his books and them on the floor.
Standing up, they immediately apologised and started to pick p some of the scattered books. As they helped to boy up, Sirius realised it was Remus Lupin. They had been placed in the same dorm, along with Frank and the hat staller.
"Sorry, we may have got... slightly lost on our way to charms and we don't want to be late" James told him. Lupin looked up and smiled hesitantly. Sirius got a good look at his features for the first time. Lupin had a light complexion, mousy brown hair, bright green eyes and three scars running from the bottom right of his face almost all the way to the top left.
"It's ok" Lupin replied quietly, "I was on my way to charms aswell: it's just at the end of this corridor." Sirius and James thanked Remus and they started towards Charms.
On the way they started up a small conversation with him. At first, Remus was hesitant and distant, but as the day progressed and they spent more time together, he began to warm to them. By the time they got back to the dorm, it felt to Sirius as though he had known his two friends all his life. And he said so, in his letter to his younger brother that night. His younger brother who was at that moment sitting in his room, writing his own letter.
Notes: I know that some of my chapters are quite short but I struggle with splitting chapters into two. I do apologise but as the years progress the chapters should get increasingly longer.