Bokura no Himitsu Kichi Daisakusen ~Escape Hitonatsu no Omoide~

Four girls, three boys, one abandoned building, no clothing! After Satoshi and his friends sneak into an old abandoned building outside of town they meet Chikako, an older girl who lives there. She convinces them to abandon their clothing and morals and have sex day and night. But when the adults in their lives come to take them back will they be able to defend their secret base?