In Ruby's scenario, Hiro is Ruby's assistant and often argues with her. He's usually the unwitting sidekick to her dangerous adventures. However, he seems to worry more about Sapphire than Ruby, most likely since he and Sapphire get along far better than he and Ruby do.
In Kurt's scenario, Hiro plays a lesser role as a messenger sent to warn Kurt about his father's assassination. He is then conscripted into Kurt's sevice for unknown reasons.
Hiro is a Strength-oriented character. However, in exchange for a lower Strength potential, he gains better defenses and versatility in terms of Skill. Despite his good elemental growth, a lack of magic growth leaves Hiro with almost no possibility of being a mage.