Mayuri is his classmate, who often attempts to coerce him into cosplaying (without much success).
Appearance & Personality
Although being biologically male, Ruka has an extremely feminine appearance, causing him much trouble (and attention) from men (even Daru was at one point attracted to Ruka's appearance). He is very slim, with thin arms and lanky body. Ruka is flat-chested.
Ruka have always dreamed of being a complete girl, and was disappointed that he was born a male. This changes later on, as Ruka was turned into a female through the influence of a D-mail, though the female Ruka does not remember being male before.
He is very sensitive and emotional, as simple sudden responses from Rintarou can cause him to cry or tremble. He likes to wear girly clothing, which caused Kurisu to confuse him for a real girl when the two met in Rintarou's lab. Rintarou even described him as "more girly than any girl, more feminine than any female" in the game.
Ruka harbors deep feelings for Rintarou, ever since their first encounter in Akihabara, when he was still a male. Later in the story, as Rintarou attempts to save Mayuri by reversing the effects of sent D-mails, the female Ruka tearfully agreed under the condition of Rintarou taking her out on a date. The date turned out awkwardly, since Rintarou was unable to be himself around her. He came to see her at the shrine and apologizes for botching the date, and the two embraces, Ruka said she would still love him even if she's no longer female.
Ruka was first introduced as an extremely feminine individual. Okabe expressed his confusion over this matter quite a few times throughout the game, and at the near beginning of the anime.
After learning of the existence of SERN and the IBN 5100 personal computer, Rintarou discovered it being stored at Ruka's family's shrine. In the alternate worldline Ruka accidentally broke it when he/she was cleaning the storehouse.
Being told of Rintarou's experiments, Ruka tells the Future Gadget Lab members a Japanese urban legend: if a pregnant woman eats more meat during her pregnancy, then her baby will be a boy, and if she eats more vegetables, her baby will be a girl. The Future Gadget Lab, although skeptical of whether or not the urban legend is true, lets Ruka send a D-mail back to his pregnant mother's pager, telling her to eat more vegetables. In episode 10, it's revealed that the D-mail has worked and the characters are transferred to a world line where Ruka becomes Rukako. ("-ko" is a common ending exclusive to female names, and therefore, would mean in that world line, Ruka has become a biological girl.) This causes an extremely awkward situation in which Okabe does not realize this and gropes Rukako's crotch in order to prove to the Future Gadget Lab that Rukako is male. He quickly learns that he's been moved to a world line where Rukako is a girl and that he's been accidentally sexually harassing her.
Later, when Rintarou attempts to achieve 1% divergence, he was troubled by the thought of reversing Ruka's wish. Ruka agreed to it, though reluctantly, after confessing her love for him and requests that he takes her out on a date. The date turned out awkwardly, since Rintarou was unable to be himself around her. He came to see her at the shrine and apologizes for botching the date, and the two embraces. Ruka then spends the rest of the day practicing with the sword Samidare along with Rintarou.
Ruka was revealed to have been in love with Rintarou since their first encounter (when Ruka was a male) and that she will still love him no matter what happens, female or not. Rintarou smiles and sends the D-mail, reverting Ruka back to being a male.
In the game, Rintarou decides not to send the mail, but helps Ruka time leap back to join Mayuri at her last cosplay convention. They would then continue to live on as lovers.
In this world line, Okabe decides not to send the D-mail that would make Ruka return to being a boy again. He convinces himself that Mayuri will still die no matter what he does and he doesn't want to sacrifice Rukako's happiness. Rukako confesses to Okabe and swears to give him (Okabe) his mother's pager number on the condition that the two go on a date together once. The two's date is deeply awkward and contrived, so much that Rukako cuts it off abruptly, leaving Okabe to guilt over it. He realizes that it wasn't truly a date because he was trying too hard to impress her by not being himself, and rushes over to the shrine where the two spend genuine bonding time together. After which, Rukako gives Okabe his mother's pager number in order to send multiple D-mails to Rukako's pregnant mother. This will cause Rukako's mother to believe that all the D-mails (including the original one sent by Rukako) to be spam, ignores them, and continuing on eating more meat, and thus giving birth to a male Ruka. Because Okabe doesn't want to turn Rukako back in a guy, he doesn't want to wipe out any memories anymore, the timeline goes on and Mayuri still dies. Realizing the devastation she has wrought, Ruka feels guilty about Mayuri's death. Remembering that Mayuri wanted Rukako to cosplay in the next convention, Rukako with the help of Okabe, leap back in time to give Mayuri at least some happiness. The plan was a success, as in that timeline Rukako, Mayuri and Okabe went to the convention together but left Mayuri's fate ultimately unchanged. The scene closes with Ruka producing the pictures they took together with Mayuri at the convention; with Okabe at peace now that he has given Mayuri some happiness. After the credits, Okabe is shown to have fathered a child with Ruka.
- Though being feminine, Ruka would always use the term "boku" to address him/herself. "boku" is the male form of addressing oneself in Japanese, so it is strange that a person like Ruka would use it.
- Ruka has an older sister, though she is only mentioned in the game.
- Though referred to as Rukako in the Japanese version, the English translation of both the game and the anime would address him/her as simply Ruka.