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“Ah, few things in nature are as misunderstood as the playful salmonella bacterium. S-Typhi is the little dickens that--”
— Hiro, mocking Kamal's cooking

Hiroyuki is a student of a medical school in the United States of America, Earth. He shares a dormitory room with fellow student Kamal Zaman. He is the more humorous of the pair, and he often makes vague innuendos that make others suggest he finds a girlfriend. Like Kamal, he is rather geeky and needs to read "How to" books to try to understand dating; however, he has a much better understanding of cooking than his roommate.