Steins;Gate[]
Luka perfoming an exorcise.
Luka was first introduced as an extremely feminine individual. Rintaro Okabe expressed his own confusion over this matter quite a few times throughout the game, and early on in the anime.
After learning of the existence of SERN and the IBN 5100 personal computer, Okabe discovered the computer being stored at Luka's family's shrine. However, later in the story on the worldlines where Luka has been changed to being female, Luka accidentally broke it when she was cleaning the storehouse on January 4, 2009.
In the anime later on, Luka overhears the lab members discussing the PhoneWave. When he reveals this to the group, Okabe hastily dubs him Lab Mem #6. In the Visual Novel, he visited the lab to test out a costume Mayuri had made and becomes appointed Lab Mem presumably to have him send a D-Mail for the sake of experimentation. Luka reveals that he actually wishes to use the PhoneWave to send a message to his mother that would result in him being born a girl. Luka 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 Luka send a D-Mail back to his pregnant mother's pager, telling her to eat more vegetables.
Okabe harasses Luka.
While it is initially unclear whether or not the D-Mail worked (because Luka still looked the same), in Episode 10 in the anime and in Chapter 4, it is revealed that the D-Mail has worked and the characters were transferred to a worldline where Luka was born a girl. This causes an extremely awkward situation in which Okabe does not realize this and gropes Luka's crotch in order to prove to the Future Gadget Lab that she is male. He quickly learns that he has been moved to a worldline where Luka is a girl and that he has been accidentally sexually harassing her while causing Luka heavy embarrassment.
Luka at the start of her and Okabe's first date.
Later, when Okabe attempts to achieve 1% divergence, he was troubled by the thought of reversing Luka's wish. Okabe explains things to Luka and while it initially upsets her, Luka agrees to it, though reluctantly, after confessing her love for him and requests that he takes her out on three dates (only one in the anime). The dates turned out awkwardly, since Okabe was unable to be himself around her. He came to see her at the shrine and apologizes for botching the date, and the two embrace. Luka then spends the rest of the day practicing with the sword Samidare along with Okabe; both of them feeling genuinely comfortable in each other's company.
Luka embraces Okabe.
Luka, who still remembered her first meeting when Okabe saved Luka from being harassed on the street, even though this memory is from a worldline where she was born male, revealed to Okabe that she had been in love with him since that first encounter that she should not be able to remember, and that she will still love him no matter what happens, female or not. Okabe smiles and sends the D-Mail, reverting Luka back to being a male.
After Okabe sends the D-Mail, changing Luka back to male, Okabe asks him if he liked him. However, Luka avoids the question by saying that he respects Okabe.
Luka's Ending[]
In this route of the visual novel, Rintaro Okabe decides in the end to not send the D-Mail that would make Luka return to being a boy again. He convinces himself that Mayuri Shiina will still die no matter what he does and he does not want to sacrifice Luka's happiness.
Okabe, Mayuri and Luka at Comika
When Mayuri does die, it leads Okabe to enter a depression. Realizing the devastation she has wrought, Luka feels guilty about Mayuri's death. Remembering that Mayuri wanted Luka to cosplay in the next convention, Luka with the help of Okabe leaps back in time to give Mayuri at least some happiness. The plan was a success, as on that worldline Luka, Mayuri and Okabe went to the convention together but left Mayuri's fate ultimately unchanged.
Luka and Okabe with their child
The scene closes with Luka producing the pictures they took together with Mayuri at the convention and with Okabe at peace now that he has given Mayuri some happiness. After the credits, Okabe is shown to have fathered a child with Luka.
Steins;Gate 0[]
Like the rest of Okabe's friends, Luka is concerned with him giving up with Hououin Kyouma persona, but is unsure how to help him.
Stray Sheep[]
As Okabe searches for Kagari around the Diet building, he runs into Luka and Faris. He ends up telling them about his search and they agree to help him. He then helps Luka cary his supplies back to the shrine. Part way through the story, an amnesiac woman named Kana comes to the shrine for assistance. Luka attempts to talk to Okabe about her multiple times, but Okabe, too focused on finding Kagari, never has a good opportunity to talk to him. Luka ends up taking her to the lab where it is revealed that the woman is Kagari Shiina, the woman they had been looking for.
Orbital Eclipse[]
Luka is one of the shrine maidens present during the New Years festival. He is also present when the armed DURPA agents attack the lab.
2036[]
After Okabe is recovered from Stratfo, he is left in a catatonic state. While Daru announces that Okabe is dead, he puts Luka in charge of taking care of his body.
Okabe holding a dying Luka in 2036.
When Okabe's past self time leaps into his future body, Luka is in the middle of a fire fight with Stratfo agents after being led into a trap. Luka is injured, but Okabe manages to reach him before he dies. Luka expresses his happiness at seeing Okabe awake before dying. This gives Okabe the resolve to go back in time and prevent this future.