Shizuka is rather timid especially given her rather quiet or mute voice which makes her rather distant from other people. However, ever since she met Rentarou she has become braver, even willing to sacrifice her own safety to help Hakari out. She is also the most modest of Rentarou's girlfriends as she doesn't like being dirty-minded. She even refused to peep on him when he was taking a bath and even tried to stop them from doing so.For a long time, Shizuka had trouble communicating with people verbally. The origin of this issue is still unknown, but to overcome it she uses books to replace talking to people, and because of that she got bullied a lot in her middle school. The problem was so severe that at one point even her mother hit her and forced her to speak. To avoid talking to people most of the time, in high school she joined the library staff where she could continue reading books without talking to anyone. One day, Rentarou, Hakari, and Karane went to the school's library to search for some books. While the two girls looked for cooking books, Rentarou tried to find something to read himself. He then met Shizuka when she reached for some books on a high shelf. After the soulmate shock, they have a short conservation and Rentarou asked Shizuka about book recommendations. She found a lot of books for him but because of the library's rules, Rentarou could not borrow them. Shizuka then gave him her personal favorite novel, which Rentarou finished in one night. The next day, Rentarou returned the book to Shizuka and noticed that she prepared the next volume for him. They then had a talk in which Shizuka explained her difficulties in communicating. Rentarou borrowed Shizuka's book again and in one week, he converted it into digital format. Rentarou then suggested Shizuka install a text-to-speech app and use it to talk with people using the book's content. The first thing Shizuka said with the app was that she loved Rentarou, which he accepted. Then Rentarou introduced Shizuka to Hakari and Karane, officially making her his 3rd girlfriend. “I like you. I'm sorry. Please do not worry about this. I'm not asking for a response, either...For I know that you are betrothed to someone. At the very least, I wanted you to know how I feel...!”