At first I was afraid of the older sister. I thought it would be the yuri insinuation that occurs in many manga. I respect those who like yuri, but these insinuations are annoying.
@Askorti: Nah, there's an older chapter where we're shown that she has what amounts to a phobia towards bugs and needed someone else to stomp it dead, so it would be more logical to take the text message at face value until proven otherwise.