Hibiki stopped singing when she heard a familiar voice, and recognized the voice belonging to none other than Ikaku, her co-worker. She waved to Ikaku smiling at his indirect compliment, and she joked a bit in response to his question, "I don't know. I hope it's not because my terrible singing made you tone deaf," She was happy that someone said that her singing wasn't awful, but she couldn't help but wonder if Ikaku suddenly did become tone deaf or if there was another reason, and if it involved with her enhanced hearing. She noticed Mio glaring at her through the window before the maid huffed and walked away. She ignored Mio and she asked Ikaku, considering she hadn't seen him in a couple days, "So how are you, Ikaku-senpai?" She usually called him by senpai because he was older than her and he worked in the bookstore longer than she did. 

She felt a shiver up her spine and she looked behind her only to see nothing. She thought someone had been staring at her, but she guessed it was only her own imagination. After she looked around, she looked back to Ikaku for his answer.
No one could see the thing that lurked nearby, because it blended in to its environment and was indirectly invisible unless someone had sensitive eyesight.