Steins;Gate - episode 18 - 02 Aug, 2011

Okabe tells Ruka about how she used to be a male and urges her to reverse the D-Mail responsible in order to change Mayuri's fate. While she initially disbelieves him, she later agrees to do so on the condition that Okabe takes her on a date. Despite Kurisu and Daru's advice on dating, Ruka and Okabe spend the evening in awkward conversation. Like Faris, Ruka eventually recalls the previous world line where she was a male, distressing her as a return to it would prevent her from pursuing her feelings for Okabe. Before sending the D-Mail that would negate Ruka's first one, Okabe realizes that the reason she did not enjoy their date was that he was trying to be someone he was not. He then returns to the shrine where she urges him to remember the time when she was a girl, to which Okabe replies that, no matter what, she'll always be his "student." With their relationship repaired, Okabe sends the text, moving back to the world line where Ruka is a guy, leaving the next D-Mail to be reversed Moeka's. (Source: Wikipedia)