Okay, first off, let’s examine Ruka’s appearance from both before and after the sex-change.  Both Rukas are similar in appearance, the slender body frame with short hair and a round face.  In fact, they’re identical.  We can assume that both Rukas are the same genetically, meaning it was the same genetic material from both mother and father.  That likely means it was the same sperm and egg that produced both Rukas, otherwise, through recombination (where chromosomes exchange various sequences between each other) and independent assortment (the ability for different combinations of chromosomes to end up within each haploid cell), we’d see a completely different Ruka.    After all, there are clues in the text to reach this conclusion.

One of the major reasons to assume this is that the text, directed to the mother, specified to eat veggies for a healthy baby.  Well, when would you start eating vegetables for a baby?  Most likely after you realize you’re pregnant would you start eating vegetables for a healthy child, several weeks after development has begun.  In fact, the step of implantation, where the blastocyst attaches to the wall of the uterus, happens roughly a week after conception.  There is the off-chance that the text could have been sent before the fertilization but that means she must’ve been on that vegetable regiment for a while.  And even then, a simple message like that would not have affected ovulation or changed which sperm was the chosen one.  Assuming these to be true, then we have the same Ruka, genetically, in both worlds.  Now how is it possible that one is male and one is female?

Alright, so according to my explanation, Ruka is the same genetically in both timelines, so how is one Ruka male and the other female?  Sexual differentiation begins roughly 4 weeks into development, when the SRY gene on the Y chromosome promotes the differentiation of the gonads into testes.  Following that step, the testes produces testosterone, the hormone more commonly attributed toward masculinity and male-features, such as muscle development and facial hair, among many others.  Testosterone is an essential factor in developing male sexual organs, and sometimes a deficiency can lead to something unusual.  Without testosterone, we are faced with Androgen Insensitivity Syndrome, a condition where male sexual organs fail to develop and female external features are present instead.  That way, the child is genetically male (XY) but with the physical features of a female instead, leading for the child to be thought of as a female their whole life (until puberty).

So why did this timeline’s Ruka develop into a female rather than a male?   After all, it’s the same sperm and egg and now we have to find a way to disable the testosterone production to a severe degree (virtually zero hormones) to lead to this syndrome.  Well, here are my thoughts.  Perhaps the text affected the mother in the way it was intended so that she consumed more vegetables.  Vegetables are notably much lower in cholesterol than meats and cholesterol is the starting block in the biosynthesis of many hormones in the human body, including testosterone.  I propose the idea that Ruka’s mother severely cut down on her intake of dietary cholesterol, which in turn reduced the amount of testosterone our developing Ruka could produce.  Keep in mind the old, male Ruka that we knew and loved was already highly feminine, leading me to believe he already had low amounts of testosterone in his body his whole life.  Perhaps the cessation of meats from the mother’s diet combined with Ruka’s testosterone deficiency resulted in a child with Androgen Insensitivity Syndrome.  While highly unfeasible that these combined efforts would be enough to change the development of the sexual organs, it is theoretically possible.  And after all, it’s a story, and what fun would the story be if it were average and commonplace.  This is Steins;Gate we’re talking about!

Additionally, there could be other explanations, too.  Suppose the message sent back in time had a different effect, one where Ruka’s mother behaved differently.  After all, the text simply told her to eat veggies for a healthy baby; we don’t know if she actually did that.  For all we know, she could’ve thought that for a healthy baby, you could enroll in a medical research project where they inject some morpholino (a molecule designed to knock out a gene and yes, I have a very heavy background in science) into her that would prevent testosterone from being produced for the baby, thus leaving us with our female-appearing, genetically XY Ruka.  But that’s even less likely.  And there are other possibilities, too, but it doesn’t matter now.

Hopefully I was able to make sense in describing how I theorize how Ruka could retain the same exact physical appearance yet be male in one universe and female in the other.  I doubt the writers spent time thinking this up, unless there were some people with a medical, clinical, biochemical, or a developmental biological background on this anime’s staff (not likely with all the physicists there, right?).  But I thought it was a fun exercise after seeing people trying to explain the drastic and shocking change of our beloved Ruka.

The tenth episode was enjoyable, especially since we spent more time with Suzuha who is one of the more fascinating and likable female characters of Steins;Gate.  Her story is seems to have the most substance and importance of all the female cast and her personality is both serious and entertaining.  I always like how she throws in jabs at Kurisu in her conversations with Okabe, such as asking about the torture from Kurisu or recalling how the only problem at the all-night party was Kurisu’s mere presence.

Also that text that Okabe got saying he’s being watched… oh how I love you Steins;Gate, for putting something like that for only ten seconds of screentime and then moving onto something else.  I can’t wait to see what happens next.