Hiro, were it not for the rare genetic marker he carries, be a miserably average Japanese salary man in a miserably average Japanese company in a miserably average world. But his world was special, he was born special, and his life has become-- extraordinary since discovering his abilities.
A dreamer in his youth and going no where, Hiro did the base minimum in most things; more interested in American pop culture, heroes and comics --from American comics to Japanese manga, Hiro coasted through most of his life as an average sort of guy. He dreamed more he did, always wanting to be special, better, something like his comics had -- he wanted to be the Peter Parker, the Kitty Pryde -- geekish, but powerful. It's how he began to experiment with certain-- anomalies in his life. He graduated high school, got a job that supported him and his comic book habit, and was reasonably content -- oir as content as a dreamer can ever really be in the 'real world'.
But there were strange things. Time-- hiccuped, sometime. Ticked backward a few seconds, and then forward; he didn't begin to seriously notice or experiment until he was in his late twenties, working in a dead end position in a Japanese company, simply doing numbers work. His skills didn't lie in his work, anyway. They involved quoting Kitty Pryde or the Fantastic Four. His memory for the fantastic was large-- his memory for his job and it's hum-drum, not so much. It's why he lived most of his life in his own little fantasy world...
...until he thought he could bring the world out. His powers were slow to develop once he started to notice the leaps of the clock and the sensation of missing time, but soon he was experimenting, even at work. His time jumping took great concentration... and he teleported. Time and space were his to command-- to a point. He would, over the course over his brush with destiny and the witnessing of a great calamity, and set himself on a Hero's Journey -- to discover his destiny and the role he would play in the world's drama -- the unfolding events leading up to the disaster he felt it was his duty to prevent.
Irrepressibly chipper and hopeful, Hiro is a gentle soul capable of great compassion. He's lousy in a fight -- as far as we've seen, anyway; his future self is scarred, goateed and carries a sword, speaks better English and emos a lot harder -- and he is skittish and uncertain. He knows that with great power comes great responsibility (and quotes Uncle Ben!) but occasionally gives in to doubt about his ability to accomplish his goals, and later is compounded by his power's limitations: While he may go back, he may visit and leave a slight impression, he cannot change the past. What's done is done, now and forever.
[Hiro Nakamura belongs to the people who made him and his source canon, HEROES; NBC, Tim Kring. I just play him at milliways_bar for fun, not profit. No infringement is intended.]