Vacation in a Room You Can't Leave Until You Have Sex

Created as a government measure against the declining birthrate and marriage rate, the "Room You Can't Leave Unless You Have Sex" came to be. The protagonist, Mutsuki, is summoned to the room during his summer vacation, where he runs into his stepsister, Tomoe, who was born from his parents' remarriage. Mutsuki is completely flustered, thinking, "She's family, after all!" But Tomoe aggressively pursues him regardless. Just when he thinks he might be able to leave soon, Tomoe declares, "I have no intention of having sex with you, Mutsuki-kun." Instead, she decides to treat the comfortable room as a vacation resort. "Can this really be called a vacation!?" Mutsuki is left utterly bewildered. Can he survive this bizarre holiday with a stepsister who claims, "I'll do anything naughty for you, as long as it's not sex!?"

(Source: melonbooks; translated)