That was a set up, Karen was waiting for Touya, she disabled the door chime and unlocked the door, than stood where he could see her with just her pants on. Touya is more upset about what happened than Karen is, she got the reaction she was expecting from him, she feels that he's getting closer to liking her, but he's still thinking of Hiiragi. Thanks for the story, I might be putting my own twist into my interpretation of the author's work, if it's not what you meant, I'm sorry.