Mayuri Shiina/Plot

Steins;Gate
Shortly after Rintaro Okabe creates the Future Gadget Lab in 2010, Mayuri was the first one to join it, as she felt that Okabe was lonely all by himself and wanted to be with him. For a few months, they both were the only ones to attend the lab, where they spent their time doing nothing of particular relevance. Some months later, Mayuri accidentally discovered the PhoneWave (name subject to change)'s hidden function, resulting in a bunch of jellified bananas, which she called "gelnanas".

On July 28, 2010, Mayuri attended alongside Okabe Dr. Nakabachi's time machine seminar. Shortly before the seminar, she managed to win a rare metal Upa out of a slot machine, but lost it a few moments later. After Okabe changes the timeline with his mail to Daru, she accompanies him in Radio Kaikan to see the crashed satellite.

Mayuri decides to visit Luka Urushibara, her friend from school, and try to convince him to do cosplay with an outfit she made, since Mayuri likes more to make outfits than to use them. As expected by her, Luka is embarrassed to do something like this, since it is a female outfit. Mayuri says the popular phrases around @channel: "Someone this cute can't possibly be a girl!" and "Cuteness is justice!", she also admires the relationship of master and disciple that Okabe and Luka have, getting excited although she says she is not a fujoshi.

She welcomes Okabe when he appears at MayQueen+Nyan², the place where she and Faris work, and says that "Okarin" and welcome ("Okaeri" in Japanese) go well together. She is the second most popular maid there due to her habit of guiding the clients by their hand. She guides Okabe to Daru's table and returns to work.

Mayuri appears later in the lab while Okabe and the others were doing experiments, and introduces herself to Kurisu Makise when she joins the lab, saying she is glad that she is not the only female Lab Mem now. However, she gets angry that they were using the food she bought to eat later for experiments, and attempts to stop them by opening the PhoneWave while it was being used. This causes an electrical discharge to occur and she is grabbed by Okabe, who is afraid to lose her. They later find out that the message they sent was indeed sent to the past, but Mayuri finds those things too complicated for her to understand and she leaves shortly after the discharge ocurred, still angry about the wasted food.

She sent a mail to Okabe about the money she uses to buy food, and he has the option to thank and promise her to buy anything she wants, which causes her to get really excited. She later finds out that Okabe and Daru were both awake for two nights, and decided to buy them some food, including Okabe's favorite udon.

After Okabe decides to hack SERN's database, Mayuri constantly complains that he is doing something wrong and decides against joining him in those type of acts.

As Okabe decides to leave the lab, Mayuri joins him asking them to have lunch. As they walk together Mayuri is suddenly nowhere to be seen, which scares Okabe. She stopped and extended her hand to the sky, her explanation is that she sometimes feels that she can reach the stars.

She calls Okabe while at work to inform him of something he wants to know. They eat on her break, and Mayuri says that she asked Faris NyanNyan about the IBN 5100 and found out that she knows something about it.

After her work she returns to the lab with Okabe and the others, but leaves shortly after.

As the Future Gadget Lab's experiments with the PhoneWave and the D-Mails proceed, Mayuri grows exponentially worried that they may be doing something wrong, but never attempts to stop Okabe. As the number of members of the lab increases, and, in particular, due to the appearance of Kurisu Makise, Mayuri starts to think that Okabe does not need her anymore, and starts worrying about her future. On August 13, 2010, as the Future Gadget Lab is celebrating the completion of the Time Leap Machine, Mayuri is killed by Moeka Kiryu during the Rounder raid on the lab. This event leads Okabe to travel back to the past to try and save her.

As Okabe's time leaps continue, he is witness to Mayuri's death a multitude of times in a variety of ways, due to Attractor Field convergence. Despite his best efforts to reach the Beta Attractor Field, he unknowingly grows distant of Mayuri, which she notices. This, alongside Mayuri's recent dreams of her own deaths, makes her belief herself to be a burden to Okabe.

Once Okabe finally reaches the Beta Attractor Field after sacrificing the life of Kurisu, Mayuri is the one to embrace him as his mad scientist façade crumbles.

On August 21, 2010, as Okabe goes back to the past alongside Suzuha Amane to save Kurisu's life, Mayuri stays behind with Itaru Hashida. After Okabe returns, wanting to give up after having accidentally killed Kurisu himself, Mayuri is the one to return him to his senses.

Epilogue
Okabe gives a Lab Mem pin to Mayuri.

Anime
In the anime, Mayuri attempts to surprise him as he is discharged from the hospital, but upon getting there learns that he already had already left. While looking for him, she runs into Luka and Moeka, both of whom received Lab Mem pins from him. Upon returning to the lab, she finds that he had also given one to Daru and left two more behind: one for Mayuri and another for someone he said would join the lab in seven years.

Isolated Jamais Vu
After attempting to find a way to save Mayuri without sacrificing the life of Yukitaka Akiha, Okabe ends up on an unknown worldline. After exploring Akihabara and trying to contact his friends, Okabe finds out that only Faris remembers him.

Mayuri, who on this worldline still works at MayQueen, does not have any recollection of Okabe. However, since the first D-Mail has never been sent, her death has been avoided. Okabe, although depressed over having lost his friends, recognizes that as a necessary exchange for Mayuri's life and accepts it.

Link of Corruption and Rebirth
As Okabe refuses to sacrifice Luka Urushibara's feelings and going back to the worldline where she was born as a man, they both are left with no other option but to accept Mayuri's inevitable death.

Several days after her funeral, Luka uses the Time Leap Machine to go back to the day Mayuri died, with the intention of making her wish of seeing her wearing a cosplay a reality.

Stardust Sky
Okabe must choose between saving Mayuri or Kurisu. Realizing that he harbors romantic feelings for Mayuri, Okabe and Kurisu decide to return to the Beta Attractor Field in which Kurisu's murder is executed as planned, but Mayuri notices that something strange was going on between Kurisu and Okabe so she decided to ask Okabe. After knowing about Okabe's journey to save her, about all people's happiness he sacrificed, and about Okabe's decisions, Mayuri cries and blamed herself, running to see Kurisu. When Mayuri encountered her, Kurisu was packing her things to go back to America. She runs and hugs her, saying she does not want Kurisu to disappear, only to hear that this was Kurisu's decision from the beginning and that she wants Mayuri to be happy; saying that Okabe loves her, she parts. After hacking into SERN's database with the IBN computer, 1% divergence is achieved. Okabe vows to remember his memories of Kurisu,and spends his time with Mayuri as lovers. On a date with Mayuri, she says she had a very important friend that she is not able to remember and that sometimes, she hears a voice, a voice that tells her to 'find happiness'. Mayuri holds Okabe's hand (doing 'Stardust Handshake') and wondering if that important friend is the reason she is with Okabe right now, saying she wants to say her thanks.

Absolute Zero
Instead of slapping Rintaro Okabe and bringing him back to his senses, Mayuri instead tries to comfort him, telling Suzuha that he would have to come to his own conclusion.

Over the next three months, she becomes worried for Okabe as he deals with his depression. During this time, Okabe, Daru, Faris NyanNyan and Suzuha all avoid telling Mayuri about her deaths on the Alpha worldline and about how Okabe chose her life over Kurisu's.

Closed Epigraph
Mayuri picks Okabe up from his hypnotherapy session. When the two reach the train station, they run into Faris NyanNyan and Luka Urushibara, both of which are thrown off by Okabe's new personality.

Recursive Mother Goose
After Kagari Shiina successfully recovers her memories after almost being hit by a truck while searching for the origin of a song she remembered, Mayuri discovers that she is her daughter from the future, and they proceed to live the several following months happily together.

However, as the time limit for the Time Machine's fuel approaches, Mayuri decides to go back to the past herself to convince Rintaro Okabe to save Kurisu Makise. Kagari, not wanting to be separated from her mother, opposes, but as she discovers Mayuri's reasoning to do so, decides to go herself alongside Suzuha. Their fate after going back to the past, however, is unknown.

Gehenna's Stigma
After being brainwashed by Alexis Leskinen and capturing Rintaro Okabe against her will, Maho Hiyajo roams Akihabara, with no clear goal in mind. She then finds Mayuri Shiina, who is looking for Okabe, and, out of her own frustration and desperation, tells her the truth about the death of Kurisu Makise and her own life. Mayuri then runs away in tears.

As Okabe wakes up after being rescued, he is informed by Itaru Hashida that both Mayuri and Suzuha have disappeared, and that the Time Machine has been destroyed.