the_debt_of_time

"Apart from my transformations, I was happier than I had ever been in my life. For
the first time ever, I had friends, great friends," he said and patted Sirius on the back. "Sirius
Black, Peter Pettigrew, and your father, Harry: James Potter."
Harry stood, still shaking, looking confused.
"Now, my three friends could hardly fail to notice that I spent every month in the
hospital wing―"
"Migraines," Sirius scoffed sarcastically.
Remus glared at him before turning back to Hermione, Harry, and Ron.
"Eventually, they figured out what I was―"
"More like stumbled upon it and got yelled at," Sirius retorted petulantly,
interrupting him again.
"Do you want to tell the bloody story?" Remus snapped.
"No, I want to murder the bloody traitor!" Sirius growled. "Hurry the fuck up!"
Remus took a slow, deep breath and continued speaking, "Instead of abandoning
me like I thought they would, my friends did something for me that would make my
transformations not only bearable but the best times of my life. They became Animagi."
"That's impossible," Hermione said, her mouth hanging open in shock. "It's not
only incredibly difficult, it's highly dangerous, and for students to attempt it... It would
take―"
"Years?" Remus smirked and nodded. "It did."
"For most of us," Sirius muttered.
"Peter, as the smallest, would slip beneath the Whomping Willow's attacking
branches and touch the notch that freezes it. Sirius and James transformed into such large
animals, they were able to keep the werewolf in check," Remus explained.
Sirius cocked his head to the side. "Forgetting something?"
Remus ignored him. "So you see, Snape's been right about me all along."
"Snape?" Sirius turned and gaped at him. "What's Snape got to do with anything?"
"He's here, Sirius. He's teaching here as well."
"I know that." Sirius groaned. "I saw his stupid face wandering the castle. I go to
Azkaban, and Snivellus gets a job offer?"
"Why does Snape hate you?" Harry asked Remus.
"Because he's a dirty, rotten, greasy git!" Sirius snapped.