Notes: This was my very first attempt at a drabble. I think I've succeeded!
Sirius had to talk to Harry. He knew what was going to happen soon. He couldn't just let things happen without warning. The only way to get in contact with Harry, at least without being caught, was through the floo. Owls could be killed, it was completely impossible to apparate into Hogwarts, and too many people knew him as Padfoot already.
He always felt uncomfortable, and hot, and ashy. And what if somebody other than Harry were to walk in the room? He'd just have to count on his timing, and hope Harry saw him through the red fiery blaze.