The true thing of why this ra** scene wasn't necessary it's not because it's ra** but more because it wasn't that well developped, if the author have really explain how Kiruko understand a new thing about the body he possess, it would have been memorable... Cause even him is confused about his body, the fact that his body sister have memory is an important information but there, no one will remember because the only we have now in head is that shi*** ra** scene !