As great as you believe a real futanari would be, such a thing would be physically impossible without massive changes to the internal body parts involved.
For example, did you know your penis is actually a few inches longer than you think it is? Your penis' starting point is internal and crosses where a woman's vagina would be, so having both body parts in the exact same location wouldn't work.
See for yourself. Note how far in the penis goes and how adding a vagina (and all the other female reproductive parts) to that wouldn't be possible.
upload.wikimedia.org/wiki.../d/d1/Male_anatomy_en.svg