His anger was explosive like a five-ton atom bomb. It would cloud all reason and judgement the boy normally had, ferocious and inefficient, attacking anyone in its way. It would disappear into nothing as quickly as it detonated, and every bit of anger he held would be gone in an instant. The fallout was just as bad, the remnants of the outburst awkwardly floating around after every incident. Everyone would shuffle around and away from him, concerned, upset, and sometimes a little frightened of him.
Tadashi used to call him 'warhead' because of this, back when Hiro was about four and his tantrums were loud and frequent. Many of his teachers marked him as a problem child because of this, and many said he was 'a walking time bomb' on his old report cards.
He knew that his temper wasn't helping anyone. It made talking to his family, the only people he could be himself with, difficult and it made him guilty to no end. He tried to calm himself by 'forgiving and forgetting', but he could never get past the 'forgiving' part first.
He started taking it out on his robots, making them more and more destructive the angrier he was, taking them to fights and obliterating his opponents. The sly rush he felt as he pocketed his earnings and ran from the thugs calmed him down somehow, and it became a habit. It continued until the night Tadashi took him to SFIT, where Hiro realized that this place could do so much for him. He worked for months on his project, far too busy to even think about going to a botfight.
When the fire broke out, Hiro was too frightened to stop Tadashi from running into the building to save his professor. The building exploded, and everything became like ghosts in the sun. When he realized that he was now an only child, he could only feel a dull ache. He never felt anger. Someone had cut his wire.
They finally cornered Yokai on his island.
"It's over, Krei," Hiro said, standing over the black-clad body.
Yokai rose, mask gone, revealing the weathered face of Professor Callaghan. His brow was furrowed, eyes bloodshot, clearly mad with an unknown grief.
"P-professor Callaghan?" He looked and sounded as dumbfounded as he felt. Tick.
"The explosion... you died."
"No. I had your microbots."
What. Tick.
"But... Tadashi...you should have died."
"Give me the mask, Hiro."
Callaghan took a step closer, looming over the boy with a venomous glare. Tick.
"He tried to save you!"
"That was his mistake!"
Hiro's heart galloped in his chest. He could hardly believe that it really was Callaghan reaching for the mask. He had been like a father to Tadashi, kind and clever, everything he had ever wanted to be. But this is who he really was. A monster. Willing to kill his own student, willing to destroy anyone and anything that would get in the way of his goal, whatever it might be. A familiar red-hot weight rested on his chest and flowed to his fists and the pit of his stomach. He finally realized what it was. Anger.
Tick. Click.
And that was when Hiro became Hiroshima.