Mayuri Shiina (椎名まゆり, Shiina Mayuri), also called Mayushii, is Rintarō Okabe's childhood friend and companion. She works part-time at a maid cafe called May Queen Nyan-nyan as a costume maid and occasionally makes cosplay outfits. She is usually the one who financially supports Rintarou's "research" when food is needed.
Mayuri is a girl with black hair and gray pupils. Her hair forms fringes that sweep from either side. Mayuri's eyebrows are noticeably thick.
Mayuri's outfit is simple and comfortable, consisting of a light blue one-piece dress and a hat of the same color. She also wears leggings underneath her clothing.
When she attends to her work in May Queen Nyan-nyan, she wears a blonde wig tied into a long ponytail.
She possesses an extremely childish and naïve attitude for her age. This may have something to do with her inability to accept the death of her grandmother when she was young. Mayuri likes to give cute nicknames to familiar people, like Rintarou (Okarin), and refers to herself as Mayushii. She often misunderstands or misphrases information she overhears from Rintarou or Kurisu, though at certain times her responses can be quite helpful. Also, Mayuri does not question Daru's perverted comments and mannerisms, or is not in any way offended by them (though this is likely because she does not interpret them as such).
Despite being socially inept, she is also responsible for Rintarou's well-being, usually tending to his needs most of the time. She's also very attentive to details, often noticing things about people that others would miss. She figured out Suzuha Amane is Itaru Hashida's daughter through the details on the Time Machine and from Daru's daily habits, suggesting a degree of skills in observation and problem-solving.
Okabe, realizing that Kurisu will need to "die" (false blood and taser, thus altering the timeline but making it so their paths do not cross) if he saves Mayuri, decides to sacrifice being with Kurisu for Mayuri's life. Kurisu decides to go along with the plan, despite Mayuri's protest, as she doesn't want Kurisu to disappear. Okabe has no choice but to send the D-Mail. Everything started again like in Episode 1, and no one has memories of Kurisu, but Okabe. After hacking into SERN's database with the IBN 5100, 1% divergence is achieved. Okabe vows to remember his memories of Kurisu, and spends his time with Mayuri. But later when Suzuha Amane comes back (with the time machine made by Itaru) to the present timeline, he goes back to the timeline of past with her where Kurisu was killed and achieves 1% divergence by manipulating the past by faking the death of Kurisu and so crosses into the “Beta“ world line. In he present timeline Okabe meets Kurisu by chance (as Kurisu wanted to thank him for saving her life and could remember the few incidents as dreams) and she could recall her love life with Okabe which continues.
Note: As per the story both of Kusiru and Mayuri live in the present timeline.
Before achieving 1% divergence, Mayuri dies in multiple ways during Rintarou's various attempts to save her, due to the events of the world lines in this same attractor field always converges into the event of her demise, though with different results each time:
- Shot in the head by Moeka Kiryū
- Ran over by a train
- Hit by the Rounders car
- Hit by a policeman's stray bullet
- Spontaneous cardiac arrest
- Mayuri's voice was used as a user guide for the Phone Microwave. According to Rintarou, it made the Microwave sound silly.
- She was the first person to discover the Microwave's "irregular" abilities when she accidentally froze her karaage while trying to thaw it. She also gave the gel-i-fied bananas the name "gelbana".
- So far, the only ending of the visual novel in which Mayuri's death is definite is Ruka's ending, as she survived in Faris's ending, Kurisu's ending (same thing applies to the True end), her own ending and Suzuha's ending (implied to have been saved through the combined efforts of Rintarou and Suzuha).
- Also, Mayuri dies of natural causes if Ruka's ending was achieved. This is the one of two instances in the plot where the cause of Mayuri's death was not an accident/murder, the other being when she goes to ComiMa on the 16th after Ruka's mail is reversed.
- Mayuri, like all other characters, has blurry memories of what happened to her in the other world lines, though unlike them she only thinks of the memories as "bad dreams".
- According to Okabe, his first kiss was with Mayuri in elementary school, though they were "just messing around."
- In one of the (failed) attempts to save Mayuri, Rintarou sent her to the past. However, instead of arriving normally, she dies and her body was gel-ified. This scene was only briefly shown in the anime.
- The gel-ified Mayuri still resembles her normal form a great deal, as the details on her outfit along with the color of her hair are still visible and her body is not distorted in any way, unlike SERN's experiments.