Feel protective as soon as Sirius hid, he very swiftly moved so he could block the boy - just in case. He'd taken a few punches to the face in his life. More than a few, actually. He could take a few more for the first person to be generous and kind to him. Luckily, it didn't end in violence. Little seemed to outside of his house.

He couldn't recall a single argument in his house that didn't end in a fist fight, honestly.

When the man went back to gathering their books, Severus turned to Sirius with fascination. "You must be very important." It was exciting. Severus smiled, unable to hide it. He was already making connections and he'd only just started. This could only go well. "You shouldn't worry, Master Black, I'll keep you safe."

He said the title playfully but with a hint of seriousness. "I'm your friend, after all."