Hiro is the Sheep of the zodiac, is a snotty, smart-mouthed brat. He's still 11 yrs. old. Despite this fact, he's actually brilliant to speak with such wit at his age.

He is in love with Kisa Sohma and resents Tohru because it seems that she monopolizes Kisa's time and attention. He starts out being hostile to Tohru, but eventually eases his initial attitude through a combination of grudging admiration for Tohru and Kisa telling him to let up. He is sarcastic and pessimistic. However, his temper and patience with Tohru is still a little unstable.

In the manga, his pregnant mother, whom seems to be just as careless and klutzy as Tohru, might just add to Hiro's annoyance of Tohru with her resemblance to his mother in her forgetfulness and childlike happy personality.

Hiro seems to have no motivation to do anything to quell the anger he causes.

Since Kisa likes Tohru, Hiro becomes incredibly jealous over her. Sometimes it seems like all he wants to do is boss Tohru around. It doesn't change much until Tohru realizes that he is going through a stage where he realizes that he is still young, and Tohru understands that it's scary to come to that realization.

His motives are to act more grown up, though he doesn't have that much self control. He's also hoping that this way of thinking would impress Kisa.