Luka Urushibara

Ruka Urushibara (漆原るか, Urushibara Ruka) is a bishōnen who looks strikingly like a girl and even wears the garment of a miko despite being a boy. He is a close friend and classmate of Mayuri and is often asked by her to try on her cosplay costumes, usually declining to do so due to his shy nature. He has romantic feelings for Rintarou because he was there to protect him from an intimidating group of Otaku that wanted to take photos in the past, stating that it doesn't matter if he is a boy or a girl. However, Ruka hides these feelings because he is a boy and he thinks Rintarou would never return them.

Due to Okabe's intervention in the form of a message sent into the past to Ruka's mother, Ruka experiences being a girl until he decided to return to being a boy after witnessing the consequences of her wish of being a girl. Rukako was his name during his time as a girl.

Ruka's Ending
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. The timeline goes on and Mayuri still dies. Realizing the devastation she has wrought, Ruka feels guilty about Mayuris death. Remembering that Mayuri wanted Rukako to cosplay in the next convention, Rukako with the help of Okabe, travels in time to give Mayuri at least some happiness. The plan is a success, as in that timeline Rukako, Mayuri and Okabe go to the convention together but Mayuri still dies. However, Okabe is okay with it, glad that he could give Mayuri some happiness.