Hiro Sohma is the Ram of the Zodiac. He is 12 years old and is in middle school, along with Kisa Sohma.
Hiro has light-brown hair and brown eyes. He is tall for his age. He is almost never smiling unless sarcastic or mischievous. He is often shown wearing a dark green shirt and pants.
He is exceedingly good at making sarcastic comments and complaining, but will get very shy and timid once around Kisa. He dislikes Momiji Sohma's hyper and carefree disposition. He isn't very fond of Tohru Honda because Kisa is drawn to Tohru who takes away their alone time. He is also very loving towards Kisa and gets very overprotective of her from time to time. He also gets jealous whenever someone is closer to Kisa then he is. Hiro also has a crush on Kisa, but he doesn't know how to express it. He told Akito that he loved Kisa, which resulted horribly in Kisa's injuries. In the series, he had despised Tohru in the beginning. He wasn't trying to hurt her, only play with her in a way.
Hiro loves Kisa more than anything in the world. They were the best of friends in elementary school. When he told Akito that he was in love with Kisa, Akito became furious. Afterward, Kisa was beaten up by Akito, Hiro knew that his confession had led Akito to attacking Kisa. While visiting Kisa in the hospital, Hiro was shocked, confused, and sad and thought it would be better to stay away from Kisa.
When they started middle school, Hiro ignored her, thinking that it would prevent her from attacks from Akito. When he found out she was being picked on by the other kids, he felt useless and was not able to do anything as it would be awkward for him to defend her suddenly after months of ignoring her.
Hiro accidentally witnessed Akito pushing Isuzu out of a window, which later causes Hiro some distress, because he found out about Hatsuharu and Isuzu dating. Hiro knew that Hatsuharu would never forgive Akito for that act if he told the older boy. Isuzu and Akito forced him not to tell Hatsuharu about the incident that Hiro had witnessed.
Before Summer Vacation
He first meets Tohru Honda while she is on her way to work. He throws his shoe onto the ground and orders her to pick it up. When she does, he begins lecturing her about always obeying orders from other people and thinking for herself.
Hiro dislikes Tohru, the very first time they meet, mainly because she is all Kisa talks about. When Hiro takes Tohru's notebook (that has a picture of her mother in it) and Tohru follows him in an attempt to get it back, Kisa appears with Momiji and asks him to give it back. He throws it at her in a response, and Kisa tells him that she "doesn't understand why you're acting this way, but it makes me sad". Hiro replies by saying, "Onee-chan, Onee-chan. That's all I hear. All you talk about is that stupid girl!" It becomes apparent that Hiro was just jealous of how close Tohru was to Kisa. After some time, Hiro grows to like Tohru, but he tries not to show it.
During Summer Vacation
When Momiji invites them to go to the summer home with them (with the invitations written on bunny stationary), Hiro complains about Momiji being so childish when Kisa told him that she wanted to go, so he accepted the invitation immediately and set off to the summer house.
Kisa and Hiro fought when Hiro rudely commented on Tohru being 'obsessed' with her mother. "She's all you ever talk about." Hiro instantly regretted it when he saw the look on Kisa's face and her saying: "Hiro, why are you always so mean to Onee-chan?" A few nights later, Hiro decides to go and apologize to Kisa, but when he opens Kisa's bedroom door, the door smashes right into Kisa's face! Kisa tells Hiro she was going to apologize to him for their fight, and then they realize they were both wrong. They both make up.
After Summer Vacation
During Sorta Cinderella, Hiro accompanies Kisa to the school. He expresses doubt at the success of the play, and was shown to be easily angered, as seen when three boys had their eyes on Kisa. He is also scared by Saki Hanajima's brother, who approaches him from behind unnoticed. When Sorta Cinderella is over, he says "Crud. What was that supposed to be?" Later, Hiro accidentally mentions Rin, and chastises himself for doing so, because he wasn't supposed to know about Rin dating Hatsuharu. However, Hatsuharu replies, "Wait. Don't tell me... you've got the hots for Rin", which makes Hiro angry.
Hiro eventually confesses to Haru that the real reason why Rin had been in the hospital for so long was because Akito pushed her out the window, angering Haru.
When Akito was about to stab her mother, she stopped when she noticed that Hiro's curse had been broken. Hiro noticed this as well, and picked up his sister and hugged her. Hiro's mother came into the room to see Hiro no longer changing into a sheep, and was overjoyed. However, Hiro interrupted her, saying that it was more bittersweet. Hiro's curse was the third to break.
Hiro loves Kisa more than anything. While Hiro is shown to be somewhat hot tempered and always making sarcastic remarks, he is shown to have a soft side for Kisa Sohma. When it is made known that Hiro loves Kisa, Akito beats up Kisa. While Kisa does not know why, Hiro does. He begins distancing himself from her feeling regretful that he could not "protect" her. When Tohru Honda becomes a sister like figure to Kisa; Hiro becomes very jealous. He does not seem to be nice to her and even gets in a small argument with Kisa.
But, the two make up. They are constantly shown together through out the other chapters. When Hiro's curse breaks, he asks Kisa if she still likes him, even though he is not "one of them". Kisa says she still does and asks Hiro if he's okay with her because she still has the curse. When Tohru was going to leave, Kisa started crying and Hiro comforted her.
Unlike most other members of the Zodiac, Hatsuharu is one of the few members to earn a honorific from Hiro (who affectionately calls him Haru-nii (Big brother Haru) which indicates them being close. There is only one time Hiro snaps at Haru and he quickly punishes himself mentally (twice) for doing so since he not only acted childishly but revealed that he knew about Haru and Rin's relationship which was supposed to be secret. In one of the side notes in the manga it is revealed Hiro Idolizes Haru (though Hatsuharu has no Idea.) it is very likely his later outfits are based.
Hiro seems to be rather close to Rin being one of the few people she seems to tolerate (although she also seems sick of him for having a loving family, to which Hiro questions why it's "wrong" to have a mother who loves him). Hiro feels guilty about what happened to Rin thinking that if it were not for his feelings for Kisa, Rin's punishment would not have been as bad. He felt like Akito timed pushing Rin out of a window so Hiro could see it and take it as a second warning concerning him and Kisa. He is one of the few Sohmas to visit Rin in hospital. He also informs Haru about what happened to Rin in hopes that he could help her, this triggers Black Haru who sets out for Akito's blood.
- Other than Akito Sohma, the person he can't stand the most is actually Ayame Sohma.
- It was revealed by Takaya-Sensei that Hiro's personality was half-stemmed from his mother's ditzy and clumsy persona saying that one day he looked at her and thought "I have to be strong".
- He is the youngest member of the zodiac (when Kisa has started Middle School he actually doesn't start until the next year, therefore he is actually a year younger than her)
- Hiro is possibly the only Zodiac member who grew up with a normal loving parent. When he was born and transformed into a sheep upon his mother's hugging him, she exclaimed "I love sheep!" and has always treated him as a normal boy, greeting him with affection and never minding his transformations. If anything, it only spurs her to hug him more.
- Hiro shares the same voice actor as Alphonse Elric in the 2003 Full Metal Alchemist anime adaptation.
- Aaron Dismuke, who was a child at the time, voiced Hiro which is very uncommon in the voice acting industry.