I Can't Tell Which Twin is Which Sex (web comic)Futago no Danjo ga Wakaranai (Pre-serialization); Futago no ♂♀ ga Wakaranai; 双子の♂♀がわからない; I Can't Tell Which Twin is Which Sex (Pre-serialization)

An 18 year old guy comes to live with his aunt and twin cousins while he tries looking for work. Although he remembers that they were twin brother and sister, he is surprised too find that they both appear to be girls when he meets them again after several years, so now he can't tell which is a guy and which is a girl.