Sirius Black Headcannon:
-so Sirius finally becomes an animagus, but against popular belief he was actually the last marauder to achieve this so when he finally turns he’s so excited!!
-running around the grounds as a dog because he’s never felt so free, when suddenly some little girl screams “ITS THE GRIM!” and people start running left right and center, and one kid is scared senseless and is just crying
-so padfoot just slowly approaches, and bows his head, and very cautiously, the kid strokes his head.
-the kid tells everyone that they shouldn’t be scared of the Grim, and slowly but surely he becomes known for something much more;;;
-whenever a kid is homesick, or bullied, or even just lonely, the Grim will find them and be their friend for a time. Sometimes they sit and stroke him, sometimes he nuzzles them, sometimes they run about and play catch, and sometimes they just sit by the fire, but he’s always there for them - it’s as if he has a way to tell when someone’s alone.
-and then one time Remus has a particularly bad moon,and Sirius ends up hurt, in the hospital wing, and everyone expects the grim to go an help him, but of course no one does.
-then one day, nervous as ever, that first little kid sticks their head around the curtain and says hello
-and sirius is like why are you here little one?
-and the kid is like “I thought maybe the grim wasn’t here because it thought you were brave? Even brave people need help sometimes.”