Barking Mad (Sirius/OC)

When the Marauders fight, fangirls cry and teachers take a breath of fresh air. "You don't mind, me sitting here, do you?" I looked up and found my crush staring down at me. "I - erh, what?" Sirius Black winked. "Good. Don't need bloody James anyway. Hi," he said, turning to me as he sat down, "be my new best frien...