Q: Why is Ruka aware that Okabe thinks she is a male? Shouldn’t the past have changed?
A: In episode 10 Okabe checks to see if Ruka is a male in the world line after Feiris sends the d-mail (World line 0.409420). In the current episode the world line is the one after Feiris’s d-mail is cancelled out (world line:0.456914) so the event where Okabe checks Ruka should have ceased to exist. However because of world line convergence a similar event may have happened in the past.
Q: What did Okabe mean when he mentioned about the “yellow thing of happiness” to Kurisu?
Q:How long does it take to walk from Akihabara to Ueno and back?
A:While Ruka and Okabe are out on a date they walk from Akihabara to Ueno then back. It would take about 45 minutes to walk the entire way.
Q:Why does Ruka have memories from another world line ?
A:Everybody has the power of Reading Steiner to a certain degree. Okabe’s reading Steiner is extremely sensitive allowing him to completely remember the events of another world line, while others are only able to have vague memories or dreams of their experiences.
Q:Why does Ruka break the IBN5100 as a female?
A:In the original game Ruka mentions as a male that he cleans the main temple instead of the storage house. While female she cleans the storage house where the IBN5100 is stored where she breaks the computer by knocking it over by mistake.
Q:Who were the waifu’s that Daru mentioned?
A:They are girls from famous dating genre games.
1.Anegasaki Nene from Love Plus
2.Fujisaki Shiori from Tokimeki Memorial 
3.Kobayakawa Rinko from Love Plus
4.Sawatari Honoka from Sentimental Graffiti 
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I want to ask something ..
*SPOILER*
I don’t understand how in faris’s ending , okabe teleported , and how he doesn’t become childhood friend with Mayuri .. and I don’t get why the world line meter doesn’t has a “zero” in the first digit .. and they didn’t reveal the content of the d-mail and they didn’t go into details all the change .. I mean , he’s sending a mail to his father right ? I failed to see how that prevents okarin from becoming friend with mayuri (they’re childhood friend , right ?)
this really confuses me . thanks
Obabe didn’t ‘teleport’. He felt the effects of Reading Steiner. Meaning that the past was reconstructed but he was able to sense the change. During Faris’s ending, they decide to find a way of keeping her father alive and at the same time preventing the IBN 5100 from leaving her father’s possession. It was successful, but as a result, many thing about the world changed and it is very likely that they moved to a 3rd world line, the Charlie world line, a world line where Okabe met neither Mayuri nor Daru. This had unexpected results, and the Divergence Meter could possibly have not been calibrated for such a change in world lines.
I am pretty sure this didn’t occur in Episode 18 but rather the VN. Please try to keep on topic
Oh yeah , and
*spoiler*
why did Rukaku wants to become a girl , again ? is it because of her sister implied in the mail ?
Rukaku is gay. He looks like a girl, acts like a girl, and likes what girls like. It’s only natural that he would want to be a girl.
I have no idea what you mean about a sister. As far as I know, Rukaku has always been an only child, in all the world lines mentioned.