There's a lot to go with here. The questions are why is Shiro hiding this body? What's underneath his clothes? Is it hot for everyone or is it really hot for him? What are these apparitions and why are they deadly? Do they have names and personalities? What are the consequences of these beings, on his environment and his psychology?

I love characters that have shadowy companions. I often write stories with them, or voices of them. It's aways fun. Anyway, here's my ending. Thanks @brisby.

You can join the fun here. There's still plenty of time to write your own ending!

Shiro

by @Brisby

Shiro paid the street vendor for his lemonade, unfazed by her curious glances to the glove on his hand. Any other day, he would have answered the unspoken questions of the smiling woman with a light quip. A bit of banter went miles in getting people to overlook his many...eccentricities.
Today though, he couldn't muster anything witty. Throngs of people were milling about the square, mindless to those who were in a hurry. His quick errand run had become a snail-paced slog behind wandering looky-loos. The brown jacket he wore was sodden thanks to the blistering bake of the summer sun. He'd give anything to shed his sweaty layers but the memories of what had happened the last time...

Compounding his exhaustion were his ever-present traveling companions. Their desperation for his attention had begun fraying his nerves since he left home. Ignoring their antics and way they clung to him had worn his energy to a hair's breadth. Sheer obstinance was all that kept him from screaming at them in the middle of the crowd.

Shuffling aside to savor the crisp drink in the shade of the over-sized umbrella, Shiro felt something crunch beneath his heel. Dammit! Whatever he had broken, it sounded expensive.

Behind him a voice shrilled, "You're paying for that!"

Shoulders slumping as he fingered his wallet, he turned. "Sorry! I didn't know...", his voice choked to a halt. Not because the person was intimidating. The blonde slip of a girl glaring daggers at him wouldn't have been able to frighten a hamster. Nor was it due to her beauty, as she had been graced with an unfortunate nose.

It was the reaction of his companions that stole his breath.

Gone were the shadowy undulations and static flickerings who had doggedly followed Shiro since he was a child. What remained were swirling vortices of crimson and pitch. Amorphous, they writhed. They wailed. The air thickened with the depth of their need.

Without warning, unctuous tendrils sprang. Shiro cried out but it was too late. Oozing with hunger, his companions snaked to envelop the girl. Her wide hazel orbs rolled to the heavens before she collapsed to the ground.

My Ending

He called them Sid and Nancy. Sid, the crimson element of his fury. Nancy, the void of emptiness omnipresent in any conscious being. The psychopath and the sociopath, respectively. Two forms that had been actors in the background of his life as dull shadowy forms, only occasionally sputtering jewels of their characteristic colors when, say, another child stole his cookie.

But Shiro wasn’t angry or depressed. He was just damn tired from the heat and the throngs.

And yet here they were, blazing full spectrum.

And they had just killed that girl. The crowd surrounded her, a few brave men trying desperately to perform CPR. But Shiro knew it was pointless. Her body might be saved, but her soul had been consumed.

Someone pushed by him, knocking his glass of lemonade out of his hand and send the plastic cup into the air. It landed square on the shirt of the largest man in the crowd, splashing sugary yellow juices on to the white linen shirts of him and his compatriots.

They all glanced in his direction. Sid and Nancy sputtered with eager anticipation. Shiro snuck through the crowds, down a brick alleyway.

“Hey, asshole!” the big man shouted. “Hey, I’m talking to you.”

“You fucker, you throw that lemonade on us?” One of his comrades asked.

Shiro shoved his gloved hands in to his pockets, continuing on down the alleyway. It curved around a corner and he was sure it would open back onto mainstreet. The day’s events had been too much, and he needed to consult his books. And Dr. Grim. Dr. Grim would have an explanation, as he always did. Worst of all, Shiro felt so hot.

“Asshole!” they continued.

Shiro turned the corner and faced an impenetrable brick wall. The side of an apartment building. He’d made a wrong turn. Behind him, the whole squad stood, waiting.

The big man had taken off his shirt, showing layers of muscle Shiro would never in his life be able to attain.

“You see this? It looks like piss. How am I goanna wear a shirt that looks like piss, fuckboy?”

“I’m terribly sorry about that. Someone knocked it out of my hand.”

The group laughed.

“I’m not asking for you to be sorry,” Bigman said. Shiro noticed his tattoos on his back now. Typical white wannabe gangsters mimicking the Irezumi style. “I’m asking how I’m supposed to wear a piss shirt. You know what? Why don’t you hand yours over?”

Sid and Nancy appeared behind the group.

“My shirt? I think its a bit too small.”

The group descended on him. “Do you think this is a fucking game?”

Shiro began to unbutton his clothes. Bigman towered over him now, smirking. Shiro opened his shirt, slipping him off.

They shrieked away.

His muscles quivered underneath, striations of ligaments a deep pink in the Australian sunlight.

“What the hell?” they gasped.

“I’m sorry,” Shiro said. The group fled into the vortices of Sid and Nancy. He’d have to have a long talk with Dr. Grim.