In case anyone else was wondering, (like myself) the girl's body is changing throughout the game I believe. Figured something was inconsistent with the multiple game cg's of Sawai Natsuha. Just got that off vndb, so if anyone could clarify on this it would be greatly appreciated.

Well, it seems the protoganist Tooru and his little sister Natsuha were both normal when they returned to their hometown. spoilerAfter a summer festival Natsuha suddenly became older/more developed during the night. Tooru needs to find a cure to return Natsuha to her younger self. Also Sumi is some kind of ghost if you didn't know yet.