I Can't Tell Which Twin is Which Sex is by Hanajiro Abe. Takushi Hatsujou had played with a twin brother and sister when they
were all kids, and he fell in love with the sister, culminating in his
asking for her hand in marriage when they grew up, to which she agreed.
However, they were torn apart for 10 years until Takushi is finally able
to get his grandfather's permission to marry her. When they finally
reunite, he is surprised to find they both look like girls. Although he
knows one of them is cross-dressing, he can't tell which is a guy and
which is a girl.
Serialization
Chapters:
Chapter 1: [Mediafire]
Chapter 2: [Mediafire]
Chapter 3: [Mediafire]
Web series
Chapter 0: [Mediafire]
Chapter 1: [Mediafire]
Chapter 2: [Mediafire]
