A 12th generation Kenkyuusei member of AKB48. She is a big fan of the idol group, especially one of the lead member Atsuko Maeda. She would get very angry with anyone who criticized Maeda. She passed the 12th generation Kenkyuusei audition because she spoke out in defense of Maeda when Minoru criticized Maeda when he was asked the question "which is your favorite AKB48 member?".
A person who dislikes sports, Hiroko is frequently tired out by the dance trainings that all Kenkyuusei members have to go through, to the extent that she injures herself frequently. However, she is also very hardworking, and she frequently stayed back after the practice sessions to continue dancing with Minoru.