Luka Urushibara (Anime romanization: Ruka) is a close friend of Mayuri Shiina and so-called protégé of Rintaro Okabe. While feminine in appearance and personality, Luka is a male in most world lines. Mayuri Shiina is his classmate, and she often attempts to coerce him into cosplaying (without much success). Although biologically male, Luka has an extremely feminine appearance, which causes him much trouble (and gets him a lot of attention) from men (even Daru was attracted to Luka's appearance at one point). He is very slim, and has thin arms and a lanky body. Luka is very sensitive and emotional. Even simple, sudden responses from Rintaro 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 Rintaro's lab. Rintaro describes him as "More girly than any girl, more feminine than any female." in the game. Luka harbors deep feelings for Rintaro ever since their first encounter in Akihabara, when he was still a male. However, Luka felt that his feelings were taboo and kept them hidden. Later in the story, as Rintaro attempts to save Mayuri by reversing the effects of the previously sent D-mails, the female Luka tearfully agreed to allow her D-mail to be undone under the condition of Rintaro taking her out on a date. The date played out awkwardly, since Rintaro was unable to be himself around her. He later visited her at the shrine and apologized for botching the date, and the two embraced. Luka said she would still love him even if she was no longer female.