As her words suggest, she's nervous, and her tension is palpable as she begins to undress the man. Nazuna-chan, a shy girl, seems docile, but she exhibits a surprising gap in her character, engaging in acts like giving a blowjob with lewd noises, which is erotic due to her otherwise quiet demeanor. This is like the typical sex with an ordinary girl who appears innocent but inexplicably seems very erotic, reminiscent of that one quiet yet oddly alluring girl in class.
