Kirino Kousaka is Kyousuke's 14-year-old younger sister.
is mature for her age and has a cold, tsundere-like personality. She has a strong "little sister" fetish and owns many adult games with older brother/little sister themes, which she got a job modeling to pay for. Despite this, she states she does not know why she started liking it, though it is suggested that she has a brother complex and is using the games as a surrogate to this. She often denies such feelings and believes the 2D and 3D worlds should be kept separate. Nevertheless, she is shown to be very frustrated when he is with, or shows interest, in other girls such as Manami who she accuses as being "all over" Kyousuke. Likewise, she frequently forces Kyōsuke to spend time with her, whether it is playing games or taking her out, but denies that she actually enjoys the time they spend together. She uses the screen name Kiririn when with her otaku friends.