Moeba is a spoiled and tsundere younger sister. And the older brother who keeps being swayed by such a younger sister. This brother and sister had a secret that only two people could not tell their parents. A dangerous play of mischief secretly performed every night after the parents are asleep. But today my parents went out and there were only two of us at home... There is no need to keep your voice down or hide anymore. There was no morals for brothers and sisters who thoroughly, generously, with all their might, and enjoyed the intense time together.