Sirius Black
The walls of the house were closing in on Sirius. Closer and closer they came, enveloping him in their dark wallpaper and hopelessness, crushing him. He couldn't breathe his lungs constricted by the walls, not enough air to fill his lungs and what little there was muggy and stank of despair. He writhed, choking.
Sirius woke to find that his sheets had become tangled around him, nearly strangling him in his sleep. The air in his room was too warm and he untangled his sheets and crept across the room to open the window and let some air in. The open window cooled the room somewhat but it did nothing to dispel the perpetual gloom that hung over 12 Grimmauld Place.
There was not enough air in this dank house that stank of despair and hopelessness. There was not enough air and Sirius was suffocating, slowly but surely suffocating. He could take it no longer. His trunk was still unpacked at the foot of his bed and Sirius grabbed it and still in his night robes tiptoed down the stairs and through the front hall. The shrivelled elf-heads cast grotesque shadows and leered down at Sirius.
The front door opened silently and Sirius slipped out and clicked it shut behind him. The street was empty and dark and deliciously cool and full of air. He gave his childhood house a two finger salute and took off at a run, feather-light trunk bumping against his thigh as he ran until he was breathless and panting.
The air in the empty park tasted of freedom. There was space here, enough space for Sirius without anyone else leering down from a portrait or his father appearing in the shadow, reeking of fire whiskey and anger. There was no deranged mother out here, no curses and angry fists, no idiot, bigoted brother, no oppressive glares and despair.
Sirius barked a laugh and waved a final two finger salute in the direction of Grimmauld Place before pulling out his wand and flicking it upwards to summon a violently purple, triple decker bus.