Remus John Lupin was sick a lot. At first Sirius never really noticed. But as the silver-eyed boy was left more and more in Remus's company, he observed the boy's sickly ways. He constantly had bags under his eyes; his complexion was always much too peaky; and there were the scars. Sirius had no idea how he missed them before—well actually he did. Remus's face was almost scar-free; it was the rest of his body that truly suffered.
No one was ever supposed to find out. Now that Sirius knew, he also knew all the measures Remus took to hide them. The one on his face—it was actually quite fascinating, Sirius thought; it ran from his eye to his jaw line—was constantly covered with cream that blended into Remus's skin. And, for the others, Remus just hid his body from everyone. Sirius wasn't ever supposed to find out; he was just walking back into the dormitory. The ebony-haired boy was half-way in the door when he noticed Remus; when he noticed a shirtless Remus.
Sirius's first reaction was one he was not proud of. His breath stopped in his throat and blood rushed to his face. Now Sirius knew beauty when he saw it—he did see quite a lot of himself, keep in mind. And Remus John Lupin was bloody gorgeous. Once his breathing returned to normal, Sirius noticed the scars. They littered his back and arms. The silver-eyed boy snuck back out the door,—though he would have been content to continue standing there—and Remus still didn't know that Sirius saw him.
So, seeing as Remus was dreadfully sick once more, Sirius was left to ponder the mysterious scars by himself. The pureblood's mind quickly wondered away from the scars and towards Remus's impeccable body.
He groaned and buried his head in his hands. Why in hell was he a half-blood? (Sirius had either forgotten that Remus was also a guy, or else he just didn't care about that as much. But, to clarify, his parents would care very much about that. In fact they'd care very much about this Lupin boy in general. But that would be another Howler for another time.)
Groaning again, Sirius decided to visit said amber-eyed youth in the Hospital Wing. Maybe he could take his mind off blood purity.

James was spread across the laying Remus's feet while Peter was struggling through his homework by the sick boy's beside. "Alright, Remus?" Those amber eyes widened a bit in surprise; Remus had never heard Sirius call him by his first name before.
"Hello, Sirius." A small smile played across the grey-eyed boy's lips. It dissipated once he saw Remus wince—all the boy did was move into a sitting position. James didn't seem to notice Remus's discomfort though, seeing as the hazel-eyed boy grinned up at Sirius.
"Well if it isn't the noble Sirius Black." Peter was the only one not looking at the young Black, he was afraid of Sirius to tell the truth—something Sirius was fine with himself, he still didn't like Peter. "Come to wish our friend a speedy recovery?" Sirius, feeling very daffy all of a sudden, bowed.
"I have come to aid Master Remus until he is healthy once more." Remus laughed heartily, which caused him to wince and grab his ribs again. This time the other boys didn't fail to notice. "Remus, what's wrong?" The sickly boy shook his head.
"It's nothing, just some sore muscles." No one was convinced. The amber boy smiled—it looked bitter to Sirius. "Really—look I can walk and everything." Remus slid out from under the sheets and stood on shaky legs. "See?" Sirius frowned (not scowled like his parents would have liked) and shook his head.
"Let us help you." So James grabbed one of the protesting boy's arms while Sirius grabbed the other. The trek to the dormitory proved to be more awkward than James originally counted on. It was hard for the three-man-wide cluster to squeeze through some corridors and crowds. In the midst of it all Peter disappeared, and James went looking for him. That left Sirius and Remus alone, looking like they were ready to enter a three-legged race.
"You can let go." Sirius did as Remus asked. "Um..t-thanks for coming down, Sirius." Sirius stopped in surprise.
"Why wouldn't I, Remus? Isn't that what friends are for?" This time Remus was surprised, but no hint of it crossed his features. "Even if you are a half-blood." Now this part Sirius hadn't meant to say at all. In fact, it was so faint he wasn't even sure if it had really slipped from his lips.
But it had. And somehow the amber boy heard it—Remus was rather far away. He stopped and turned with narrow eyes. "So this is what it's been about," he hissed. "The noble and pure Sirius Black can't bear to be around lowly half-bloods?" Sirius winced even though Remus hadn't touched him at all.
"It…it was." Remus turned back around and started to walk again. "Wait! Remus, wait!" The other boy continued to walk, but his pace had slowed considerably. "It was Remus, was!" Sirius felt his face flush as he tried to find the right words. "I know this doesn't mean much to you, but I've been trying. It's hard fighting something you've been taught your whole life." Remus finally stopped, but he kept his back to Sirius. "I don't want to hate you, especially not over something as ridiculous as this."
"It's not something I have any control over." The smaller boy began talking over Sirius. "I can't pick my blood, Sirius." Before Remus could continue—and before Sirius could fully think it through—the pureblood enveloped the half-blood in a hug.
"I know. And I can't control what my parents tell me." The smaller boy's face was a brilliant scarlet by now. "I'm sorry, Remus."
"I'm sorry too, Sirius." The pair stood like that for a few more moments.
"Poofs!" That is, until a few Slytherins stumbled upon them.
"Rictusempra!"
"Tarantallegra!" Sirius and Remus walked away as the Slytherins battled with their respected jinxs. Sirius smiled.